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Lecture Comments (15)

1 answer

Last reply by: Dr Carleen Eaton
Thu Apr 28, 2016 10:59 AM

Post by Kristy Osborne on April 17, 2016

Am I able to skip ahead of the lecture all I want to listen to is tolerance.

1 answer

Last reply by: Dr Carleen Eaton
Wed Mar 26, 2014 6:36 PM

Post by Fadel Hanoun on December 8, 2013

You are amazing!

1 answer

Last reply by: Dr Carleen Eaton
Wed Feb 20, 2013 4:18 PM

Post by bo young lee on February 5, 2013

i keep dont know the how endocrine system and immune system and lymph system differences

0 answers

Post by Matt F on January 16, 2013

Girl you blowin' up! yew!
Sick vids, thank you.

1 answer

Last reply by: Dr Carleen Eaton
Sun Oct 21, 2012 10:32 PM

Post by Sarah Wilson on October 20, 2012

These videos are wonderful, thank you.

1 answer

Last reply by: Dr Carleen Eaton
Thu Jun 9, 2011 6:32 PM

Post by Daniela Valencia on June 4, 2011

Dr Carleen,

love your videos!! :))
Great teacher.

Thank you!

3 answers

Last reply by: Dr Carleen Eaton
Wed Apr 20, 2011 4:10 PM

Post by Billy Jay on April 19, 2011

Hi Dr. Eaton,

Is the term "Lysozyme" a generalized word used to describe sugar-degrading enzymes. The reason I ask is because around 10:40 you mention that Lysozymes are contained in Lysosomes, but I can't find any online source to confirm that. However, various sources do say that amylases (among other types of enzymes) ARE found in Lysosomes. I was wondering if they're they same thing.

The Immune System

  • The first line of defense is barrier to entry. The skin, mucus membranes and tears are barrier defenses.
  • The second line of defense includes nonspecific cellular defenses such as neutrophils, macrophages and natural killer cells. Proteins such as complement and interferon also play a role in nonspecific defense.
  • B cells are produced and mature in the bone marrow. B cells are responsible for humoral immunity, which is mediated by antibodies secreted by plasma cells.
  • T cells mature in the thymus and are responsible for cell-mediated immunity.
  • Cytotoxic T cells destroy cells that are infected by a pathogen or that are abnormal.
  • Helper T cells assist in activating the production of antibodies by B cells and by stimulating cytotoxic T cells.
  • Antigens are presented to T cells by Major Histocompatibility Complex (MHC) Molecules on the surface of cells.
  • Passive immunity is conferred when an individual is given pre-formed antibodies. Active immunity requires the stimulation of a person's own immune system.

The Immune System

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • The Lymphatic System 0:16
    • The Lymphatic System Overview
    • Function 1
    • Function 2
  • Barrier Defenses 3:41
    • Nonspecific vs. Specific Immune Defenses
    • Barrier Defenses
  • Nonspecific Cellular Defenses 7:50
    • Nonspecific Cellular Defenses Overview
    • Phagocytes
    • Neutrophils
    • Macrophages
    • Natural Killer Cells
    • Inflammatory Response
    • Complement
    • Interferons
  • Specific Defenses - Acquired Immunity 20:12
    • T lymphocytes and B lymphocytes
  • B Cells 23:35
    • B Cells & Humoral Immunity
  • Clonal Selection 29:50
    • Clonal Selection
    • Primary Immune Response
    • Secondary Immune Response
    • Cytotoxic T Cells
    • Helper T Cells
  • Major Histocompatibility Complex Molecules 40:44
    • Major Histocompatibility Complex Molecules
  • Helper T Cells 52:36
    • Helper T Cells
  • Mechanisms of Antibody Action 59:00
    • Mechanisms of Antibody Action
    • Opsonization
    • Complement System
  • Classes of Antibodies 1:02:45
    • IgM
    • IgA
    • IgG
    • IgE
  • Passive and Active Immunity 1:05:00
    • Passive Immunity
    • Active Immunity
  • Recognition of Self and Non-Self 1:09:32
    • Recognition of Self and Non-Self
    • Self-Tolerance & Autoimmune Diseases
  • Immunodeficiency 1:13:27
    • Immunodeficiency
    • Chemotherapy
    • AID
  • Example 1: Match the Following Terms with their Descriptions 1:15:26
  • Example 2: Three Components of Non-specific Immunity 1:17:59
  • Example 3: Immunodeficient 1:21:19
  • Example 4: Self-tolerance and Autoimmune Diseases 1:23:07

Transcription: The Immune System

Welcome to Educator.com.0000

Today, we will be focusing on the immune system.0002

And the immune system protects an organism from viruses, bacteria, pathogenic protists, chemicals and even cancer.0005

We will begin by talking about the lymphatic system and then, going to specific cells and proteins that are part of the immune system.0018

The lymphatic system is a network of vessels much like blood vessels in the circulatory system.0027

But, it is actually a separate network that does link up to the main circulation, and it is a network of vessels that contain lymphatic fluid or lymph fluid.0033

Lymph fluid is formed from interstitial fluid.0044

So, interstitial fluid, recall, is fluid that is outside the vessel spaces, so it is outside the blood vessel in the tissue spaces of the body.0050

And lymph fluid is derived from that.0066

In addition to the vessels and lymphatic fluid, lymph nodes, the spleen, the thymus, the adenoids and the tonsils are all part of the lymphatic system.0070

The functions of the lymphatic system are twofold. The first function is for the lymphatic system to return interstitial fluid to the circulation.0084

So, interstitial fluid ends up in the lymphatic vessels, and eventually, the lymphatics meet up with venous circulation in the upper body near the neck.0104

So, then, the lymph fluid, which is derived from interstitial fluid, ends up back in the circulation.0114

In fact, if there is a problem with the lymphatic system, there is a blockage, or sometimes lymph nodes need to be removed, like if a person has cancer,0121

that can cause edema or swelling, which is caused by fluid in the tissue spaces.0129

So, if there is a problem with the lymphatics, let's say under the arm, in the armpit, there are lymph nodes,0134

if some of those are removed, the result can be that the person's arms swells up because there is fluid that cannot be drained.0139

The second function of the lymphatic system is the one we are going to focus on right now.0148

And that is, it functions as part of the immune system. It functions in immunity.0153

Lymph nodes and other lymph tissues contain cells called lymphocytes, and lymphocytes are extremely important in the immune system.0159

Lymphocytes are found in lymph tissue.0172

So, your lymph nodes in your neck, you might find that if you get sick, if you get an infection that involves your head or neck, your throat hurts.0177

Or you get a cut on your face that is infected, that the nodes in your neck become swollen.0186

And that is because the lymph nodes are doing their job where they are scanning that lymphatic fluid that comes through.0193

And if they find an invader, they find a pathogen, they are going to react to it, and they will swell up.0199

So, they function in immune surveillance and in immunity.0206

Now, this is just to give you an overview of what the lymphatic system is, but we are going to talk about many other components of the immune system.0211

And we are going to start with the most general and what is the first line of defense, so I am going to talk about three lines of defense.0218

And the first line would be to keep the invader out, keep the bacteria or the virus or even the chemical out of the body.0226

Before I talk about barrier defenses, I want you to know that there are two broad categories of immune defenses: non-specific and specific.0237

Non-specific includes barrier defenses. These are the first line of defense.0254

There are also non-specific cellular defenses and proteins that function in defense.0261

These are the second line of defense, and then, specific defenses constitute the third line of defense. These are T and B cells.0272

So, non-specific defenses, as the name suggests, do not just target a single type of virus or single type of bacteria.0280

They either target any type of invader, like the skin keeps out...0288

It does not check and see is there a virus or a bacteria or a dust particle. It keeps it all out- non-specific.0293

Even cellular defenses that target many, many types of bacteria or many types of viruses are considered non-specific.0300

Specific means it is really only targeting a very, very particular organism.0308

OK, so, three layers of defense, the first line of defense is barrier to entry.0312

The obvious one is the skin, which is a barrier to entry. It keeps out infectious agents, chemicals, viruses, bacteria, all of that.0321

However, there are other aspects of barrier defense. One is the mucus membrane.0333

Mucus membranes line the tubes in the body that are open to the outside. Remember that the respiratory tract is lined by mucus membranes.0338

The gastrointestinal tract is lined by mucus membrane, the reproductive tract, and these all open to the outside.0351

Looking, for example, at the respiratory tract to give you an example, we breathe in particles.0360

And they make it past the filtration in the nose, and they get into the airway.0370

These particles like dust can become trapped in the mucus that lines the airway.0374

And then, cilia will sweep that mucus up and out, so the particles are expelled out.0380

So, mucus membranes are important in blocking entry of particles into the body.0387

Some other barriers to entry are things like tears. Tears wash pathogens out of the eyes.0397

So if you get dust in your eyes, your eyes will tear up. They will water, and they will flush out whatever is trying to get in.0406

Enzymes called lysozymes are present in the saliva, in the mucus and in the tears.0415

And they are hydrolytic enzymes, so they can break down things like bacteria.0426

pH also plays the function in barrier defense as the acidic environment in the stomach and in the urine kill bacteria that end up in those areas.0433

There is also a fairly low pH. Sweat has a fairly low pH.0454

So, the skin, it keeps the pH on the skin lower, so that also helps to kill bacteria or pathogens that land on the skin.0460

Alright, so, this is the first line of defense- barrier.0471

So, a pathogen - I have been using that word - is a disease-causing organism.0476

Let's say that the pathogen gets past the barrier. It gets into the body.0480

It is going to come into contact with the second line of defense, and these are also non-specific.0486

It is a bit of a misnomer, though, because non-specific cellular defenses do have some discretion.0493

For example, they might target bacteria, not just a particular super specific strain.0500

They might target something on a bacterial cell that many, many bacteria have.0507

But, they are non-specific compared to what we are going to talk about in a few minutes with the T and B cells.0512

So, this is sometimes also called...the barrier and the cellular defenses, the non-specific defenses are also sometimes known as innate defenses.0520

They are there. They are ready to go.0530

They are fast acting versus the other name for specific defenses is acquired defenses or acquired immunity, the Innate immunity.0532

And let's use the word immunity and acquired immunity.0543

So here, we are talking about innate. It is sitting there.0549

It is ready to go, and because non-specific defenses do not have to recognize a very specific organism, they can respond quickly.0552

They do not have to wait to be activated. They just respond.0566

A very important component of non-specific defenses are the cellular defenses.0569

Phagocytes are cells that can engulf and destroy invaders such as bacteria, other microbes, viruses.0577

So, what they do is they engulf pathogens. They engulf other substances as well, but I am going to focus on pathogens.0590

They engulf pathogens, and then, the pathogen is in a vacuole; and the vacuole that whatever these cells engulf,0602

so the cells...here are some bacteria floating around, they are engulfed by the cell, and they end up inside the cell in a vacuole.0613

The vacuole will fuse with the lysosome, and remember from the lecture on cell structure and subcellular structure that lysosomes contain lysozymes.0622

And inside, now, the vacuole has fused with this lysosome, and you end up with these, the lysozymes in here.0635

The lysozymes inside the lysosome can, then, cut up that bacteria, hydrolyze it.0651

So, phagocytes engulf pathogens. They contain them in a vacuole that fuses with the lysosome.0662

Lysozymes inside the lysosome destroy the microbe.0669

Talking about particular types of phagocytic cells, some types of leukocytes or white blood cells are phagocytic cells,0674

specifically, neutrophils, macrophages and natural killer cells- these are often called NK cells.0686

Neutrophils respond to chemical signals that are released by infected cells.0705

If a cell has been infected, let's say a bacterium releases chemical attractants,0713

and the chemical attractants cause the neutrophils to go to the area where the infected cell is; and it will ingest the microbes at that site.0728

Macrophages are derived from a type of white blood cell called a monocyte.0736

They patrol the body and ingest bacteria and other pathogens. So, one of their functions is that they go around and patrol the body.0743

Others are just stationed in a certain area. For example they are also located in the lymph nodes.0752

So, I mentioned lymph fluid is going to go past the lymph nodes.0762

If there is some problem in there, there is a bacterium, then, the macrophage is ready to go ahead and engulf that.0766

Natural killer cells are lymphocytes, so these ones are actually lymphocytes - these two are leukocytes - that recognize infected cells.0776

So, if a cell has been infected by a virus specifically, they will lyse them. They will cause the cell to burst.0802

I just want to clarify, too. All of these are derived from white blood cells.0820

So, they are all leukocytes, but natural killer cells are derived specifically from lymphocytes. OK, they are a type of lymphocyte.0827

Now, we have talked about phagocytic cells and the cellular part of non-specific defense.0843

There are other aspects to non-specific defense that rely very heavily on proteins.0854

First, I am going to talk about the inflammatory response. The inflammatory response does involve cells but involves some important proteins, as well.0862

In the inflammatory response, when inflammation occurs, histamine is released, and mast cells release histamine.0869

The effects of histamine are that it causes blood vessels to dilate and become more permeable, so, I am going to put "they become leaky".0882

They become more permeable.0897

As a result, fluid leaves the blood vessels. Fluid enters the tissue space.0899

So, let's say you have a cut, so you have this cut here in your hand; and what is going to happen is organisms and pathogens0911

could come into the body as a result of that cut, and then, the mast cells will release histamine, and let's say that this is a blood vessel.0925

Let's say this is your skin here, and you got a cut; and now, these mast cells are going to cause a release of histamine.0934

It is going to act on the blood vessels, and there are these red blood cells going through, and there is fluid.0941

And fluid is going to leave the vessels and going to the tissue space, which is one of the reasons why when there is an infection, an area swells up.0945

Now, why is fluid even coming out? How is this helping the situation?0955

Well, this fluid actually contains molecules that attract phagocytes to the area.0960

So, histamine is released at the area where there has been a problem, where there is a possible infection.0969

The blood vessels dilate. They become leaky.0976

Fluid leaves the vessels, goes into the tissue space, and this fluid contains molecules that attract phagocytic cells.0979

Therefore, if a bunch of bacteria has gotten in through this cut, now, neutrophils and macrophages will come to the area and clean it up.0997

Symptoms of infection are attributable to this inflammatory response.1007

Everyone has had an infection, some kind, and since blood flow to an area that is infected increases, what happens is the area swells up.1013

And then, because of this fluid coming out, the area also becomes red and warm.1024

In fact, pyrogens can be released. So, pyrogens are released by macrophages, and they increase the temperature.1030

So, you might get a fever when you have an infection.1038

What they actually do is they cause the hypothalamus to reset the body's thermostat, so the body temperature increases.1041

It is not really well-understood how this fights infection, but it is believed that bacterial growth is inhibited somehow by this increased temperature.1051

So, anyways, symptoms of infection are attributable to the inflammatory response.1059

Non-specific cellular defenses include the actions of phagocytic cells.1065

They include the inflammatory response, which ends up in bringing phagocytic cells to an area where there is a problem.1072

Also, there is a couple of other proteins that you should be familiar with, and that is complement and interferons.1079

These are important parts of the non-specific defense system- second line of defense.1090

Complement is a group of proteins. Complement proteins are found in plasma.1098

So, complement proteins are found in plasma, and they can become activated and then, lyse or burst cells.1104

So, if the cell is infected, or some type of cell that has a problem, they can go ahead and lyse it.1113

Interferons are proteins that help protect the body against spread of a virus, a viral infection.1121

If a cell is infected by a virus, it secretes interferons, so let's say this cell has some viruses in it. It is going to secrete interferons.1135

And what these interferons are going to do is they are going to go and tell nearby cells watch out there is an infection around.1147

So, these cells nearby can, then, synthesize substances that will help prevent them from being infected.1158

This limits the spread of infection, and then, another part of the immune system can get rid of this infected cell, as well, to prevent the spread of infection.1167

So, we have covered non-specific defenses, barrier defenses like the skin,1177

cellular defenses such as neutrophils, macrophages, natural killer cells that can engulf viruses, bacteria.1183

We have talk about the inflammatory response, which brings these cells into the area where there is an infection.1193

Finally, we talked about a couple of sets of proteins that function as non-specific methods of defense.1200

The other half of the equation is the specific defenses, and these are also known as acquired immunity.1208

And you will see why they are called acquired immunity because they need to be triggered.1215

They need to recognize a certain pathogen before they really get going.1221

Specific defenses take longer to be activated than non-specific defenses, but they are an extremely powerful and important part of the immune system.1228

These constitute the third line of defense.1237

T lymphocytes or T cells and B lymphocytes constitute the specific defense system or acquired immunity.1243

Lymphocytes are a type of white blood cell, so they are produced in the bone marrow. There are three types of lymphocytes.1253

There are T cells. There are B cells, and there are natural killer cells that we already talked about.1264

So, these natural killer cells, I said, are part of the non-specific defense system or innate immunity.1273

Here, the T and B cells are the other two lymphocytes. They are part of specific immunity or acquired immunity.1281

We are going to go into each of these types in detail, but to just get you started now, B cells are produced in the bone marrow; and they mature there.1295

So, they are produced and mature in the bone marrow.1306

T cells are produced in the marrow, but they mature in an organ called the thymus- produced in the marrow and mature in thymus.1314

T and B cells are capable of recognizing certain antigens.1334

Antigens are molecules that elicit a response by the immune system, so antigens elicit or trigger a response by the immune system.1340

These are often proteins. For example, a protein on the surface of a bacterial cell could be an antigen and not necessarily even the whole protein.1359

It may be just a certain part of the protein. A little structure is part of this protein that is recognized by a T or B cell.1370

Now, what is extremely important is that there are millions of T cells and B cells, and they recognize different antigens.1377

So, one B cell might recognize a certain part of a protein on Streptococcus.1385

And then, there is another B cell that only recognizes a certain part of a protein on staph infection, a certain subtype of staph infection.1393

So, they are very, very specific.1402

But, there are millions of these, which allow our bodies to protect against almost any possible pathogen that is thrown at us.1404

Now, we are going to start with B cells and then, go on talk about T cells and then, put everything together.1415

B actually stands for bursa, and that has to do with the way B cells were discovered.1423

But, what you should really remember when you think of B is bone marrow because these cells are created and mature in the bone marrow.1429

B cells are responsible for humoral immunity, so B cells- humoral immunity.1440

And then, what you need to contrast that with is cell-mediated immunity when we talk about T cells.1447

T cells, we say, it is a cell-mediated response, and when we say humoral immunity, what we really mean is that these cells produce antibodies.1457

Another word for antibodies is immunoglobulins.1469

Now, how do B cells and T cells recognize a particular antigen?1479

I am going to focus on B cells, but a lot of what I am saying, the general concepts hold true for T cells.1487

We have a B cell, and it has a bunch of receptors on it, and T cell also have receptors called T cell receptors.1496

So, I am focusing on B cells. I have a B cell, and right here are the B cell receptors.1503

When these are secreted, they are antibodies. They are antibodies.1510

A B cell that is turned into a plasma cell can secrete antibodies, so they can go out and bind to antigen.1517

Right now, we are going to focus on a B cell that has these receptors attached.1524

Now, here is the structure of the B cell receptor, which could be an antibody if it is secreted.1528

And what you will see here is that it consists of a heavy chain, two heavy chains and two light chains.1535

Within these heavy and light chains, there are regions called constant regions. These are the dark regions here, constant.1544

Right here, it is a light region. I will just put C, C, C and variable regions at the end.1553

Now, if there is a cell that this is attached to, this part of the heavy chain is going to be in the cell membrane.1563

It is a transmembrane region, and as you can imagine, you cannot just have any structure and have it work inside the hydrophobic cell membrane.1570

It has to be a certain structure.1580

So, it is important that this region is constant and has a certain amino acid sequence.1581

Also, there are these disulfide bonds that hold the heavy and light chains together, and these regions need to be constant so that, that bonding occurs.1587

So, we need constant regions where there is this bonding or its transmembrane.1601

On the ends, though, is really important because that is the antigen-binding site.1605

And there are just almost infinite combinations of what the antigen-binding site can be like.1610

The shape of the antigen-binding site differs from T cell to T cell from B cell to B cell.1618

So, one B cell might have an antigen-binding site shaped like this, and then, if an antigen came along that was roundish, it would fit here.1625

There could be some other B cell receptor that has a different shape, and then, this antigen would not bind; but another antigen might bind.1634

This is what is responsible for the huge diversity of the ability of the immune system to recognize the tremendous diversity of antigens.1647

It is because these antigen-binding sites are different on various cells.1658

So, how is this diversity created at the molecular level? Well, it is through gene rearrangement.1663

Gene rearrangement allows for variation in the antigen-binding site.1671

What I want to be clear, though, is that in one B cell or one T cell, the antigen-binding site is going to be the same for every receptor.1688

It is not like this B cell is going to have one receptor with this shape and then,1697

another receptor that is like this and binds with a different antigen and then, another one that is more like this.1702

It does not work that way. All the receptors on that single B cell will focus on one antigen.1707

So, that is because of how the variable regions were arranged on the DNA.1715

They can rearrange, form different combinations in the light chain and then, in the heavy chain.1722

And those two get put together, and it can come up with just all different shapes.1727

Now, another B cell will have rearranged its DNA differently.1731

And then, it might have some antigen-binding sites that look like this, and on that cell, they are all going to have that same shape.1735

So, one B cell is going to have just a certain type of antigen that it binds to.1742

But, if you put all the B cells together, there is a huge repertoire of what antigens can be recognized.1747

Alright, the important message here is that B cells and T cells have receptors on them that allow them to bind to antigens,1759

and that each B or T cell has a slightly different receptor, which allows them to recognize different antigens and put together...1771

There are just many, many, many millions of possibilities for what these cells can bind to so that our bodies can recognize different invaders.1780

Clonal selection describes what occurs when a particular B cell or T cell recognizes an antigen.1792

So, as I said, there are millions of different kind of receptors, all these different B cells and T cells that recognize various antigens.1803

But if there is a certain infection, what we need is to have many, many, many of the B or T cells that recognize that certain infection/pathogen.1812

Let's focus on B cells right now. So, B cells can recognize antigens that are on a cell, and they can also recognize just free antigens.1824

An example would be there is a bacterial cell. Let's say there is a bacterial cell, and it has these certain proteins on the surface.1839

And a B cell can, then, come along and possibly, depending on the shape of its receptor, recognize one of those.1848

Bacteria also secrete toxins. So, the bacterium might secrete some protein shaped like this or like this that a B cell could recognize.1858

So, let's say that this B cell does recognize some antigen that is out there, and it goes along and then, binds to that antigen.1867

What will occur is that the B cell will be stimulated, and it will proliferate. Proliferate meaning it makes many, many copies or clone cells.1879

So, there will be many clones. Each of these clones will have the same antigen receptor.1899

It will also be able to fight this type of bacteria or virus or whatever it is recognizing.1906

So, if a B cell recognizes an antigen out of all the millions of B cells, there are certain ones that will recognize the antigens from a particular infection,1915

those will be able to bind to the antigen, and they will be stimulated to divide, so B cell recognizes antigen. The B cell binds to the antigen.1924

Therefore, that particular B cell will be stimulated, and it will proliferate. By proliferate, I mean that it divides and creates thousands of clones.1950

Since they are clones, they can also fight that bacterial infection or that viral infection.1970

There are two types of cells that are created from the stimulation of that original B cell.1979

One is plasma cells. The other is memory B cells, so memory cells and plasma cells.1989

What plasma cells do is they secrete antibodies.2003

So, they secrete antibodies, which means that now, there is going to be thousands of these plasma cells secreting antibodies that recognize this antigen.2008

And there is always bacteria running around loose in the body. These antibodies will get it.2021

The memory cells like plasma cells, they carry this type of antigen receptors.2025

So, they recognize this particular antigen, but they do not do anything right away.2033

What they do is they stick around for years and even for the rest of a person's life creating what is called immunological memory.2038

Now, these plasma cells have an immediate effect. They are going to go, and they are going to fight this infection.2047

These do not. They are just going to hangout and wait in case that infection occurs again later on.2053

These plasma cells or what plasma cells are is a type of effector cell.2058

So, plasma cells are one type of effector cell. I will talk about other types in a minute.2063

There are two phases or types of immune response.2069

The primary immune response is mediated by effector cells such as plasma cells. In B cells, these are plasma cells.2074

So, if you get sick, if you are exposed to some kind of pathogen, and you get sick, you are going to first have a primary immune response.2094

And B cells that recognize the antigen on that will be stimulated. They will proliferate.2106

They will create these clones, and the plasma cells will secrete antibodies to fight that infection; and then, you will get well, OK.2113

This response peaks about 2 weeks after an infection and then, drops.2123

If you get that same infection later on, let's say you had the chicken pox, and your body responds;2132

and all these B and T cells are activated, and you get over the chicken pox, and then, ten years later, you are around somebody with the chicken pox,2140

you now have memory cells sitting in your body that will recognize the antigens on that chicken pox or varicella virus. It is called the varicella virus.2149

Anyways, memory cells will be sitting there, and they are ready to go. You have already got thousands of these clones that recognize chicken pox.2161

So, things are just sitting there ready to go. This is the secondary immune response.2172

And you see why we call this acquired immunity because it takes this stimulation by a particular antigen, and you need to build up this immunity.2181

The secondary immune response is mediated by memory cells.2188

You are going to be able to respond more quickly and more strongly the second time around.2201

And so, you may not even end up getting the chicken pox the second time, or maybe you will just get a much lighter case.2206

So, this pool of memory cells is what allows for what we call immunological memory.2214

And it is why for certain types of infections, if somebody gets it, they may not get it again.2224

Even for the rest of their lives, these memory cells could hang around.2233

Now, memory cells are the basis of most types of vaccination, and we are going to talk about that later on.2237

But, just keep in mind that you could end up creating memory cells by getting an infection, having a bacteria, virus in your body.2246

It stimulates the production of memory cells.2253

Or you could be vaccinated with an antigen that will cause you to produce2256

memory cells even though you have not gotten sick and actually caught an infection.2262

I want to just briefly address T cells in general before we go on and talk in detail about2273

T cells and how they are stimulated because T cells also undergo clonal selection, as well.2279

As I said, T cells form in the bone marrow and mature in the thymus, and they are responsible for cell-mediated immunity.2286

There are two types of T cells.2300

One type are cytotoxic T cells. These are also called killer T cells.2304

The second type are called helper T cells, and the names really tell you what they do. Cytotoxic T cells destroy cells that are infected or abnormal.2314

If a cell is infected, and then, the cytotoxic T cell recognizes "well, there is something wrong with this cell".2337

It will produce perforin, which creates pores in the cell membrane and causes the cell to lyse, so killer T cells kill infected cell.2347

Helper T cells do not have a direct action in destroying an infected cell or destroying a bacterium or destroying a virus.2360

They have a very, very important indirect action, multiple indirect actions.2368

What they do is that they help to activate. They have a key role in activating cytotoxic T cells and inactivating B cells.2373

So, they help these other parts of the immune system become activated.2388

Now, like B cells, T cells have antigen receptors on their surface. They have a huge variety of types of antigen receptors.2393

And if they come into contact with a particular antigen that they recognize and can bind to, they will be selected.2405

They will undergo proliferation, and many, many clones will be created; but the way in which this occurs is different.2412

So, B cells can go, and they can recognize an antigen that is floating around loose. It is a protein that was secreted.2420

They can recognize an actual bacterial cell with certain cell surface proteins.2427

So, they just go around, and they are directly looking at these antigens. T cells do not do that.2431

In T cells, antigens need to be what we call presented. They need to be shown to the T cell in a very specific way.2435

And this requires what we call the major histocompatibility complex molecules, or frequently, they are just known as MHC molecules.2445

Fundamental point is that T cells only recognize antigens that have been presented to them, shown to them in a certain way.2457

They do not just recognize a bacterial cell floating around or a protein floating around. They have to have the certain structure.2477

Now, what does presentation of an antigen mean?2486

It means that a cell has broken down an antigen, and then, the antigen is bound to a molecule called major histocompatibility complex.2490

The antigen is, then, displayed on the surface of that cell.2505

Now, let's say that this cell has internalized an antigen. It could be a regular body cell that has been infected by a virus.2510

It could be a macrophage that has engulfed bacteria doing its job and then, broken down this bacteria.2521

So, somehow, there ends up being this foreign protein inside this cell.2530

This cell is going to break it down, take little pieces of the antigen and display them on the surface via this MHC.2536

And so, this cell has all these MHC molecules with various antigens displayed so that T cells can go around and check out what the cells are displaying.2548

Now, what is important to realize is that while there is certainly foreign proteins could be displayed, and they can cause a reaction with T cells,2568

some of the proteins that are displayed are body zone proteins.2580

So, if this cell broke down an old structure and a macromolecule, and it broke it down to get rid of it or recycle it,2583

it could display pieces of that on the cell surface.2592

What is going on with this MHC is it is a reflection of what is going on inside the cell.2597

What is going inside the cell is a lot of normal activities, but there could be problems too.2602

Now, if all the cell is doing is just displaying its normal proteins, the T cells are not going to react. They are not going to bind.2607

They will only bind if there is a foreign molecule that they have the right T cell receptor to recognize.2614

To get a little bit deeper into this, there are actually two types of MHC molecules: class I MHC and class II MHC.2629

Almost all body cells...I am just going to put "all body cells have class I".2642

There are a few exemptions like red blood cells do not have MHC class I, but almost every cell in the body has these.2651

So, that allows nearly every body cell to show T cells what is going on.2659

Class II MHC molecules are only found in very specific types of cells, so they are only found on what is called antigen-presenting cells or APCs.2668

Some types of antigen-presenting cells, so antigen-presenting cells examples...these are phagocytic cells.2689

They are macrophages. They are B cells.2697

B cells are actually a type of antigen-presenting cells and so are another type of white blood cell called dendritic cells.2702

So, just starting out with the MHC class I, almost every cell in the body has these.2710

And if a cell in the body gets infected, it ends up with internalizing this bacteria where a piece of a bacteria, it breaks it down.2717

It presents it on the surface, and let's say this is MHC class I.2728

So, along with all of these normal molecules being presented, there is also this antigen, this bacterial or viral or some other type of protein.2736

Or it could even be a protein from the cell that is abnormal.2747

And there is a lot research being done on this, but in general, the immune system is thought to be able to also recognize cancer cells.2754

The immune system recognizes what is a normal body substance, material protein and will not attack that.2765

But, if the structure is wrong, which happens with cancer cells, they produce abnormal proteins sometimes.2772

That may be recognized as an antigen, the same way a pathogen would be.2777

So anyways, regular proteins and body substances are ignored.2781

But, if there is an antigen here, and out of all the millions of T cells, this one recognizes that antigen, it will use its T cell receptor to bind.2786

Now, remember I said there are two types of T cells.2798

Cytotoxic T cells can have antigen presented to them by class I MHC.2804

So, the type of MHC that is found on every body cell is recognized by cytotoxic T cells.2822

Cytotoxic T cells are also called CD8 cells, and this is because of a material that they have on their cell surface called CD8.2832

And CD8, this is going to be the CD8, and this is a cytotoxic T cell.2849

The cytotoxic T cell has CD8, and CD8 can bind class one MHC; so CD8 binds class I MHC. Meanwhile, the antigen receptor binds the antigen.2868

So, what this does is it helps the two cells to stay together. This cell, let's say, has been infected by a bacteria.2894

It is displaying a protein that is foreign to the body.2901

The cytotoxic T cell comes along. It uses the CD8 to help it stay near the cell because the CD8 can bind the class I MCH.2905

The antigen receptor recognizes and binds to the antigen, and after all this, what happens, this cytotoxic T cell is activated.2915

So, in the same way that clonal selection occurs in B cells when they recognize an antigen,2924

clonal selection occurs in T cells when they recognize an antigen.2934

The big difference is that in T cells, these antigens need to be presented by MHC molecules.2939

Now, I have focused here on cytotoxic T cells. What about helper T cells?2946

Helper T cells are a bit different. Helper T cells do not bind MHC class I.2952

They bind MHC class II, bind class II MHC.2971

Helper T cells are also known as CD4 cells, and just how I said that the CD8 can recognize class I MHC, CD4 recognizes class II MHC.2979

Remember that class II MHC is only found on the special antigen-presenting cells.2997

So, if an antigen-presenting cell like a macrophage ingests a foreign molecule and presents it on class II MHC, helper T cells will be activated.3004

Those helper T cells have CD4 on their surface that allows them to associate with the class II MHC.3016

Then, a T cell receptor on a particular T cell can recognize an antigen. That T cell will be stimulated and will make thousands and thousands of clones.3023

So, T cells just like B cells encounter an antigen, antigen plus MHC.3035

A T cell that is specific for that antigen will proliferate just like the B cells do and make thousands and thousands of clones of two categories.3046

B cells have effector cells and memory cells.3062

So, when a B cell is activated, when it is selected, it proliferates and creates plasma cells that secrete antibodies.3068

Those are effector cells and memory B cells.3075

When T cells are activated, they will proliferate and create clone, thousands and thousands of cells. Some of these will be effector T cells.3078

They will be helper T cells that will go out and do their job right away.3091

Or if it is a cytotoxic T cell, they will be cytotoxic T cell effector cells that go out and start lysing sick cells in the body- infected cells.3094

There is also going to be this big pool of memory cells, of memory helper T cells and memory cytotoxic T cells.3105

So, the next time you get an infection, you will have this whole store of helper T cells3113

and cytotoxic T cells and B cells that are all memory cells that are ready to go.3119

OK, so, clonal selection is fundamentally the same, the principle in T and B cell.3125

But, the details differ because T cells must have antigen presented to them.3132

I do want to note that class II can also present two cytotoxic T cells.3137

So, class I and class II can present two cytotoxic, but class II is the only one that can present to helper T cells.3148

Now, I want to focus more on the role of helper T cells. They have their name because of their key function in activating B cells and cytotoxic T cells.3156

So, They help to activate cytotoxic or killer or CD8 all the same T cells and B cells.3168

I say help to activate because just having a helper T cell around is not activated helper T cell is not alone going to activate cytotoxic T cell or B cell.3184

These will still need to recognize a specific antigen to be activated, but the helper T cells play a very important role.3196

So, let's say that a macrophage or other antigen-presenting cell ingests some bacteria and inside, ends up with this bacterial protein.3206

It breaks that down, and then, it eases its class II MHC to present that antigen on its cell surface.3227

Helper T cell comes along that has an antigen receptor, a T cell receptor that recognizes that particular antigen.3239

This helper T cell will then be stimulated, and it will produce some effector T cells; plus it will produce memory T cells.3251

And for simplicity, I just showed the same one continuing.3270

But, it actually could be these effector ones that are, then, going on and stimulating cytotoxic T cells and B cells.3273

So anyways, the helper T cell becomes activated because it recognizes an antigen presented by a class II MHC molecule on an antigen-presenting cell.3280

As a result of that, a couple of things will happen. This APC is going to secrete cytokines.3292

Cytokines are small proteins. These cytokines will, then, stimulate the T cell, the helper T cell.3304

The helper T cell, in turn, will also secrete cytokines, and it is these cytokines that are going to help activate both cytotoxic T cells and B cells.3316

The cytotoxic T cell, in addition to the cytokine stimulation, is going to have to encounter a3340

cell that has been infected and is presenting an antigen that it recognizes for it to bind to.3347

So, there is an antigen. So, here is an infected body cell, infected cell, and it is presenting an antigen here via MHC class I.3360

The T cell receptor on this cytotoxic T cell is able to bind to that antigen.3369

Now, under the influence of cytokines and the stimulation by recognizing that cell, the cytotoxic T cell is going to become activated.3374

It is going to undergo clonal selection. Cytotoxic T cells are going to produce perforin.3384

They are going to, then, be able to kill infected cell. They are going to be able to do their job.3391

Meanwhile, B cells that have been activated also need to encounter antigens that they recognize. They will be activated.3397

They will create plasma cells. Those plasma cells will secrete antibodies, which will attack the antigens.3407

So, the helper T cell is going to play a role in activating both cell-mediated immunity and in the...3413

so, the cell-mediated response by these cytotoxic T cells and the humoral response, the antibody response by B cells.3429

Now, I have simplified this. It is a bit more complex with the B cells because what the B cells end up needing to do3439

is they do not really just get these cytokines that are secreted and float over.3451

They actually need very close interaction with the helper T cells. Remember that B cells are also antigen-presenting cells.3456

So, they have class II MHC on them, and they, therefore, can present a particular antigen and present that antigen to the helper T cell,3464

activating the helper T cell, which will cause cytokine secretion to activate the B cell.3476

The bottom line, though, is that helper T cells secrete cytokines, and they activate both cytotoxic T cells and B cells. They are part of what activates that.3483

So, cytotoxic T cells, cell-mediated immunity, lyse cells. B cells work via humoral immunity.3501

They secrete antibodies. Helper T cells help both of these to function.3511

Clonal selection causes a pool of effector cells to go out and start fighting the infection, T cells, cytotoxic T cell, B cells, right away.3517

That is the primary immune response.3529

Memory T and B cells are there in case the infection recurs later on. That is the secondary immune response.3531

Now, I have talked about how cytotoxic T cells can create pores and cells and lyse these cells, but how do antibodies work?3540

How do they kill microbes? How do they kill pathogens?3550

Well, there are multiple mechanisms. One mechanism is to block the attachment of the pathogen to the host cell.3554

Let's say there is a bacteria, and it has these antigens sticking out; and it has receptors that allow it to bind to the host cell.3563

So, it binds to the host cell and then, infects, so this is a bacterium; and this is a host cell.3579

And what the bacteria wants to do...except the host cell will actually be a lot bigger than the bacteria.3587

But, the idea is that the bacterium uses some type of receptor to possibly bind to the host cell and infect it.3591

What antibodies can do is they can bind, and they can then block.3602

For example, if this receptor is bound by an antibody, it is not going to be able to bind to the host cell.3611

So, one mechanism of antibody action is binding the surface of the pathogen.3616

The antibodies attach to the surface of the pathogen. Then, the pathogen cannot attach to a host cell.3624

The virus or bacteria cannot attach to the host cell because it is being blocked by antibodies.3631

A second way that antibodies work is called opsonization.3636

In opsonization, antibodies bind to a pathogen. They bind to a microbe, so these antibodies are secreted.3640

They are floating around. They will recognize a virus or bacteria, and they bind to it.3649

Opsonization, what it refers to is that this binding of antibodies to a pathogen facilitates the phagocytosis of a pathogen by macrophage.3654

So, often times, if a microbe has antibodies attached to it, it makes it easier for the macrophage to engulf, recognize and engulf these pathogens.3669

And sometimes the antibodies actually cause the bacteria or viruses to form a big clump, and then, the macrophage just engulfs that whole clump.3681

So, it facilitates...opsonization facilitates phagocytosis of the microbe.3690

So, one mechanism is to block the microbe from attaching to the host cell. Antibodies can do that.3704

A second mechanism is for the antibody to facilitate the phagocytosis of the microbe.3710

A third mechanism that antibodies use is to activate the complement system.3718

What antibodies do is they trigger a series of events that results in the formation of what is called a membrane attack complex.3724

And the membrane attack complex can lyse a cell.3738

So, antibodies trigger the system. The system goes through a bunch of cascade at this whole series of reactions.3743

And then, a membrane attack complex is formed that will lyse the invading cell.3751

So, bacteria or viruses in the body will be either inactivated or eliminated by antibodies.3758

There are actually five classes of antibodies, and they are listed here; so I am going to tell you some major features of each.3766

One thing is that the same cell can produce various types of antibodies but at different times.3774

And each of these has a slightly different structure and role.3780

IgM is usually the first one produced, so it is the first type of antibody that gets secreted in response to an antigen.3783

And these antibodies are slightly different in their structure, OK?3802

So, IgA is found in secreted fluids like saliva, so it is found in saliva.3806

It is found in tears. It is also found in breast milk.3817

And we are going to talk more about the idea of antibodies being in breast milk, for example, and then, being passed on to a newborn.3823

IgG is the most common type of antibody, and it is a type that can cross the placenta; so this protects the fetus.3835

IgE stimulates the release of histamine from mast cells and basophils.3854

Therefore, IgE plays a role in allergies, so if you have, let's say, Hay fever for example.3871

We talked about the inflammatory reaction and how histamine causes blood vessels to dilate and become more permeable.3877

The result is if the blood vessels in your nose dilate and become permeable, you will get a stuffy nose. You will get a runny nose.3884

So, the symptoms of allergies are largely attributable to IgE.3891

I have talked a little bit about immunization, and I want to talk more about it and the concepts of passive and active immunity.3902

I just discussed that IgA is found in milk, so it is found in breast milk.3913

And if a baby nurses, the baby breastfeeds, the baby will ingest antibodies.3920

This is a type of passive immunity. What passive immunity means is that an individual is given preformed antibodies.3926

It is passive because they are being given the antibodies.3936

Their B cells do not need to make those antibodies. They are just accepting the antibodies passively.3939

This confers temporary immunity on the newborn while their immune system is getting and going and developing and getting up to speed.3947

So, it is a temporary measure. It is also very rapid.3957

As soon as you give someone antibodies, they have got that. They are there.3961

They are working. They are preformed.3965

However, it is temporary. In days or weeks or even months when antibodies are broken down and eliminated from the body, that immunity is gone.3967

Another example is IgG crosses the placenta. This is a preformed antibody being given from the mother to the fetus and conferring passive immunity.3979

Sometimes people need some help. They need quick help to fight an infection, and one way is administering immunoglobulins.3995

You might hear about the term immunoglobulin injection or gamma globulin. It is also called gamma globulin.4005

And what this is, is pooled IgG from various people that is given to a person who needs some immune system help.4013

And it is also a form of passive immunity if it is given in this way.4021

So, if you make your own IgA or your own IgG, that is active. You are making it.4026

But if these are given to someone, then, it is passive. If you make your own, it is active.4030

So, a gamma globulin injection, IgG that goes from the mother to the fetus or IgA that is ingested by a newborn via breast milk,4039

these are all passive immunity. It is fast acting, but it is temporary.4048

Active immunity requires the stimulation of a person’s immune system. In active immunity, your own cells are making the antibodies.4054

Your own T cells are killing invaders. Nothing is being given to you.4063

Active immunity can result from stimulation of the immune system by an infection, and it is long lasting.4069

It is mediated by memory cells, so if you acquire an infection, and your body makes memory cells, you may be immune for life to certain infections.4081

So, passive immunity will fight that infection then and there, but it is passive. It is being given to you.4096

Active immunity is your own body reacting, and it is long lasting. An infection can cause active immunity as you fight the infection.4102

Immunizations can cause active immunity, immunization with an antigen. An immunization could contain a killed organism that has antigens on it.4113

But, it will not make a person sick, then, because it is dead or a weakened organism or even recombinant proteins.4127

So, you do not really need to have the whole bacteria/virus to elicit an immune response. You just need that little tiny antigen fragments.4137

So, now, a lot of immunizations are made by just creating recombinant proteins in the lab, and those are enough to elicit an immune response.4142

What an immunization is doing is it is letting your body see what the antigens on a certain bacteria or virus look like.4150

Your body gets ready. It makes all these B cells.4159

It makes these memory T cells, and then, later on, if you are exposed to the infection,4161

you are going to mount a secondary response because your body has already seen the infection.4165

Now, a concept that I mentioned but that we did not delve into is the idea that B cells and T cells recognize foreign antigens.4173

They do not go around, or they should not go around attacking the body's own substances.4183

So, on MHC class I, a cell is showing a T cell. All these different proteins and substances and materials is displaying on its surface.4187

And some of these are the body's own materials, but the T cell does not attack those.4198

B cells do not go around just attacking different body proteins usually. Why is this?4203

Well, during development of lymphocytes, during development of B cells and T cells,4209

those B cells and T cells that have surface receptors against body proteins are eliminated.4216

So, they go through what we sometimes call education, that the T cells and B cells are educated.4225

And what it really is, is that during development, B cells and T cells are shown somehow various proteins and substances and materials from the body.4231

And those that are self-reactive that have receptors that are shaped so that they will bind to the body's own materials, are eliminated.4241

And therefore, once the immune system has matured,4250

the only T cells and B cells that are left are ones that have receptors that will not react and bind to the body’s own structures.4255

What we call this is self-tolerance. T cells, B cells, they tolerate the body's own substances, materials and molecules.4267

They tolerate it. They ignore it.4280

They do not react to it because those cells that would react to it have already been eliminated.4281

Now, autoimmune diseases are a result of failure of self-tolerance.4287

What happens in autoimmune diseases is that T and B cells, the immune system,4294

fails to differentiate self-from non-self, at least with specific proteins, for example, type I diabetes.4304

In type I diabetes, the body ends up attacking cells in the pancreas- the beta cells in the pancreas.4320

Something about those is not realizing "hey, this is self". Instead, it is attacking it, so it is an invader.4333

In multiple sclerosis, the immune system attacks the myelin sheath on neurons. It thinks the myelin sheath is an invader.4340

There are cells in the immune system that bind, attack, activate, and that is going to cause neurological impairments,4352

the impairment of the function of the neurons because that myelin sheath is needed to conduct the signal along the axons.4361

Rheumatoid arthritis, lupus, these are all examples of autoimmune disease.4370

So, it is very important that the body knows self from non-self.4376

The immune system may not recognize a protein on a cancer cell as self because that protein, as I mentioned, may not be shaped normally.4381

There may be something different about it.4391

So, self, it strictly defined, would mean not only it is your own proteins, but is the normal ones.4392

And again, it is not completely well-understood how this all works.4399

But, self versus non-self may also play a role in the immune system protecting us from cancer.4401

Another problem that can occur with the immune system is not attacking oneself but immunodeficiency.4409

This means that an individual's immune function is diminished.4416

We sometimes say the person is immunocompromised, so their immune system is compromised.4422

The result is that the person will be at increased risk of infection. They cannot protect themselves in the usual way.4428

Medications can cause this. A big example is chemotherapy.4436

Some drugs used to treat cancer may suppress the bone marrow. Certain ones suppress the bone marrow.4440

The bone marrow is the site of lymphocyte production, and therefore, a person whose bone marrow is suppressed is at increased risk of infection.4447

There are congenital, so inborn, conditions.4458

Some people have where they are not producing enough lymphocytes. These individuals are immunocompromised.4461

AIDS: AIDS is caused by the human immunodeficiency virus, HIV, and HIV infects helper T cells.4468

Not only does it infect them, it hides within these T cells.4478

As we discussed, helper T cells are needed to activate the immune system, B cells and cytotoxic T cells.4484

So, individuals whose helper T cell count is decreased, they do not have enough helper T cells, are immunocompromised,4492

then, they are more likely to get certain infections.4502

When someone is immunocompromised, even what to us would be a minor infection, can be life threatening.4508

Or organisms that to us may even live in our bodies, they are just, they are there,4515

they do not bother us, could cause serious symptoms in someone who is immunocompromised.4520

Beginning with example one, match the following terms with their descriptions.4528

Cytotoxic T cells: antibody-secreting cells formed from clones of activated B cells.4533

T cells do not secrete antibodies. B cells secrete antibodies, so that is incorrect.4543

Do they recognize and destroy cells infected by pathogens?4548

Well, cytotoxic T cells are also called killer T cells because they kill infected cells, so this is a good answer so far.4554

Display antigens via class II MHC. Include B cells, macrophages and dendritic cells.4563

Cytotoxic T cells are not one of these cell types.4572

They do not use class II to display antigens or secreted by helper T cells, stimulate B cells and cytotoxic T cells. Well, this does not make sense.4576

Cytotoxic T cells are not secreted by helper T cells. In fact, B is correct.4586

Cytotoxic T cells have the job of recognizing and destroying cells that are infected by pathogens.4592

Antigen-presenting cells: are these antibody-secreting cells formed from clones of activated B cells?4600

Do they display antigens via class II MHC? Do they include B cells, macrophages and dendritic cells?4609

Are they secreted by helper T cells, stimulate B cells and cytotoxic T cells?4618

Well, antigen-presenting cells present antigens, and they do it via class II MHC molecules, which are recognized by helper T cells.4625

B cells, macrophages and dendritic cells are all APCs.4635

Finally, we have cytokines and plasma cells.4643

Cytokines do not secrete antibodies. In fact, cytokines are proteins.4647

They are proteins that are secreted by helper T cells among other cell types, and then, they go on; and they stimulate B cells and cytotoxic T cells.4651

The helper T cells secrete cytokines. Those cytokines, then, can stimulate other cell types in the immune system.4662

Finally, plasma cells are antibody-secreting cells that are formed from clones of activated B cells.4670

Example two: list three components of non-specific immunity, and describe their functions.4680

Well, there are many. We could first list some of the barriers, the barrier defenses.4686

So, they asked for three: skin, mucus membranes, tears, saliva, the acid or low pH in the stomach, in urine.4692

These are all components of non-specific immunity, and their function is to prevent entry of pathogens into the body.4712

The second group...so, I asked for three components. You could have gotten three components right here.4728

But, there are many more part of non-specific immunity that also occurs within the body.4734

And components of that are phagocytic cells, for example, neutrophils, macrophages- natural killer cells.4740

The function of these cells is, these are all...actually, let's do this one at a time.4764

Neutrophils are phagocytic cells, and they ingest microbes. They ingest pathogens, so they are phagocytic cells that ingest pathogens.4771

Macrophages: they also ingest pathogens, and a part of their function is to patrol the body looking for pathogens.4785

They are also situated in organs like lymph nodes.4792

Natural killer cells lyse infected cells and cancer cells.4797

Some other components of non-specific immunity are the inflammatory response.4808

The inflammatory response, one major function is to attract phagocytic cells to infection sites.4814

The release of histamine causes permeability of the vessels so that fluid from the vessels ends up in the tissues at the site of an infection.4831

And that attracts neutrophils and macrophages to the area.4839

Complement: that is another part of non-specific immunity, and it is a group of proteins that can lyse cells. The function is to lyse cells.4844

Finally, interferons play a role in protecting cells against viral infection.4854

An infected cell will secrete interferons that will warn nearby cells and prevent the spread of that viral infection.4866

So, these are all...I said list three. There are many more than three that you could have listed.4875

Example three: why might an immunization be less effective in an individual who is immunodeficient?4881

Well, recall that immunization relies upon immunological memory, and it is active.4888

So, active immunity results when a person's immune system is stimulated to produce antibodies.4896

And active immunity or the stimulation of one's immune system also relies on memory cells. Memory cells also result from immune system stimulation.4924

Without the memory cells, immunization will not work. There will not be a pool of cells ready to respond the next time around.4948

If somebody is immunodeficient, what they have is decreased immune function and a decreased number or functioning of T cells and B cells.4956

So, no matter how much you show them the antigen, no matter how much you give them this antigen, try to immunize them,4973

if their T cells and B cells are not going to respond, they are not going to be protected by the immunization.4979

Finally, example four: describe the relationship between self-tolerance and autoimmune diseases.4988

Well, self-tolerance refers to differentiating between self and non-self-molecules, and with cell tolerance, the immune system ignores self molecules.4994

It recognizes this is a normal body molecule and does not attack it.5023

So, an autoimmune disease means that there is a failure of self-recognition, and that the immune system attacks self-molecules.5032

That concludes this discussion of the immune system here at Educator.com.5061

Thank you for visiting.5066