Immuno - Lec 22

7/31/2019 Immuno - Lec 22

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Infections and Vaccines

Dima Bani-Eisa

Ziad Al-Nasser

Tuesday, 2/8/2011

20

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Immunology Lecture #22

Tuesday, 2nd of August, 2011

2nd of Ramadan, 1432

!..... ....

So keep your spirit high, have faith and say: Ya Rab!… And here we GO :D

Yesterday we were talking about infections and vaccines and I told you how efficient some of

the vaccines are like smallpox (which is eradicated completely), poliomyelitis, diphtheria and

pertussis.

We said that microorganisms when they enter our body usually they cause disease and some

of them are so evasive they manage to deceive our immune system to inflict injury and our

body fights back. And the idea of having vaccination is just to cut out the first stage which is

the primary immune response, so instead of exposing patients to the wild-strain that cause the

disease, we could give , or , and those

are going to stimulate the immune response, and when we give a booster dose we stimulate

the memory cells and those stay in our body for a longer period of time.

Sometimes we could give the products of the immune system where we call thator and this could be artificial where we make the

antibodies outside the body (monoclonal antibodies), get them from animals, get them from

vaccinated people or from people who were infected in the past. So if you got bite by a rabid

dog, you might be getting rabies, so immediately we give you passive vaccine. OR it could be

natural like the passage of immunoglobulins from the mother to the baby through the

placenta (IgG) or through the first *colostrum (IgA).

* Colostrum: is a form of milk produced by the mammary glands of mammals in late pregnancy.

Most species will generate colostrum just prior to giving birth. Colostrum contains antibodies toprotect the newborn against disease, as well as being lower in fat and higher in protein than

ordinary milk.

The passive from of vaccination has nothing to do with memory; they don't induce memory,

they just neutralize the viruses, the toxins or the bacteria, and the only thing that induces

memory is when we actively induce the immune system; either naturally when we get infected

OR artificially you challenge the immune system by antigens. So the idea if we are exposed to

any of the infectious agents then these infectious agents are going to be neutralized by these

antibodies we get from the passive vaccine and then the complement is going to be activated

and ADCC mechanism could be activated as well.

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Types of vaccines

Live Vaccines

They are the most effective because: they replicate and thus deliver sustained doses of

antigen. They replicate intracellularly so they deliver antigenic peptides to MHC class I and

thus stimulate cytotoxic T-cells. They replicate at the anatomical site of infection which

further focuses the immune response, like in polio in the GIT where we'll get IgA antibodies.

They cause which describes a form of immunity that occurs when

the vaccination of a significant portion of a population provides a measure of protection for

individuals who have not developed immunity, and where the vaccinated people could infect

other people with a good vaccine.

We could face two problems with the live-attenuated vaccine: the viruses may

spontaneously revert to the virulent wild-type organism that causes the disease. In patientswith immunodeficiency where they can cause infection despite attenuation. So in Medicine

we DO NOT give live-attenuated vaccines to immunodeficient people and we don't give them

to pregnant ladies as well.

We attenuate microorganisms usually by sub-culturing them till they lose their virulence or we

could use strains from animals that they share lots of antigenic determinants with the wild-

strain, like in the live-attenuated vaccine of smallpox we use the vaccinia virus which causes

cow pox in animals. Also when we use bacilli Calmette-Guerin ( vaccine, we don't use

mycobacterium tuberculosis, we use stains of mycobacterium bovis.

Killed Vaccines

Here we kill or inactivate the microorganisms either by heat or by chemicals. It is less effective

than the live vaccines, but it is safer, where we expose the patient to all parts of the

microorganism, and we call this "cellular". But we can use the "acellular" type where we don't

have to use all the cellular components; we could use the component that is responsible for

the disease, and this is the . So it has some side effects, the reason we switch to

the acellular type.

Subunit Vaccines

They are excellent and depend on the part that is causing the disease; they could be either the

attachment proteins that are what we really want an immune response against, so viruses and

bacteria could be neutralized. Or if the disease is caused by toxins, we get the toxin and

inactivate it into and then the immune response is going to neutralize the toxin.

They have noticed that all these vaccines go through the extracellular pathway of trafficking,

so in order to have the cytosolic response and presentation with MHC class I and then

activation of cytotoxic T-cells, we have to introduce those intracellularly.

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Here in subunit vaccines we can use the DNA vaccines introducing the DNA of the antigenic

determinant that we want intracellularly, so it can produce proteins and be trafficked by the

cytosolic pathway and then the antigen will be presented by MHC class I.

Failure of this type of vaccines could be due to or . The viral factors

like when the virus is changing its antigenicity or structure because of mutations, like what we

have with HIV, it has hundred of mutations, that is why vaccine industry fails to produce a

vaccine for it. And the solution for that is by using multiple peptide forms, like what we do for

influenza viruses, and it should be updated, so that all the changes of antigenic variants are

included in the vaccine. The host factors like for example some HLA allelic forms that don't

bind. [the doctor explained it as that but you can refer to box 24.4 page 195 in the book for further

explanation].

Here Dr. Ziad started reading the table above and added:

The most famous one in the live-attenuated vaccines is the oral polio (the three strains:

1, 2 and 3). And we have the MMR (measles, mumps and rubella) the three in one shot.

When to use that, it depends on the prevalence of the disease. For example; in the first

world country they use those after the first year, at the 15 month of age nearly, they give

the MMR once, while in the third countries where it's more prevalent they use it little bit

earlier, maybe at 9 months of age. For influenza we have two types of vaccines; either live-attenuated or killed.

We use BCG in the third world countries.

The experimental canary pox as a vector for HIV, where here we use viruses as carrier

molecules then we can integrate some of the HIV antigens into the canary pox and inject

that into humans.

We inactivate the diphtheria toxin with formalin to become a toxoid.

We could be using the polysaccharides of encapsulated microbes, where the problem

here is that these polysaccharides are not that immunogenic, so we have to hook themwith a protein conjugate, and we call those , like streptococcus

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pneumonia and haemophilus influenza type B, so that they can induce thymus-

dependant antigens and activation of T-helper cells, while the polysaccharides alone

induce thymus- dependent antigens. Look at the figure below:

If you are exposed to the polysaccharide antigen it's going to act on the B cells without

memory; only IgM antibodies of low affinity will develop. But when you hook it into a

protein conjugate, the conjugated protein will be presented with antigen presenting cell

stimulating the T helper cells to produce cytokines and activate the B cells to switch into

higher affinity IgG and to produce memory cells. So the conjugated vaccine are much

more efficient compared here to the non-conjugated or if we use the polysaccharides

alone.

We can use recombinant peptides, like in hepatitis B surface antigen, where we

genetically engineer the gene that codes for the hepatitis B surface antigen in yeast, so

the yeast can make the hepatitis B surface antigen.

Adjuvants

Toxoids in general need a substance to enhance their antigenicity, so we use Adjuvant.

Adjuvant is a substance that enhances the immune response.

How a substance can enhance the immune response? If you remember, we said we could mixit with oil, so its release to our body will be slow and the exposure to the lymphoid cell will

take a longer period of time. The second thing is by mixing it with a substance that stimulate

macrophages (the acute phase response, the alert signals).

is an adjuvant which can stimulate the macrophages to produce

cytokines that are needed for the stimulation, but it's not a powerful one, and two new

approaches are being used to create improved adjuvants: The unmethylated cytokine and

guanine sequence (CpG) motifs stimulates the Toll-like receptors.

Those are micelles of lipid and subunit antigen that are lipophilic andable to penetrate cell membranes.

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Other vaccines like dead and subunits don't have T-cytotoxic cell response; because they get

phagocytosed by APCs and they go through vesicular type (extracellular pathway), so how

they are going to stimulate T-cytotoxic cells and make the presentation by class 1 MHC

antigens? By:

1) Immunestimulatory complexes (ISCOMs): We put the virus or the antigen inside them

and expose them to the cytoplasmic membrane, and then they will fuse to the

membrane then go intracellularly, so they can be presented by class 1 MHC. And it's

used at the GIT or the respiratory tract.

2) we can use retroviruses or adenoviruses. Retroviruses are RNA viruses,

they have an enzyme called reverse transcriptase, they change from RNA to double

stranded-DNA then DNA gets integrated into the chromosome. So we can have one of

these viruses and put the gene that we want the cell to code for into these retroviruses,

for example, then it will infect the cell. So it's going to transfer the DNA inside the cell

and the cell will translate that particular gene to a protein product.

3) we could inject the DNA itself inside the cell so it will code for the

antigen we want and it will be presented through class 1 MHC.

So now why we are using the intracellular vaccines? What is the aim? Why we are using these

mechanisms? Simply to stimulate T-cytotoxic cells, presentation with class 1 MHC antigens.

Vaccine Schedules

Those are the programs that we have in the developed world and the developing world.

You know hepatitis B is sexually transmitted disease and it is very common in third world

countries and nowadays we start with hepatitis B vaccine for our children. Also we give

children triple vaccines, for example DPT vaccine: diphtheria, pertussis and tetanus.

The most common vaccines that we use in our part of the world are BCG, DPT, Haemophilus,

polio, and Measles.

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Bordetella pertussis causes the Whooping cough. The vaccine for whooping cough used to be

cellular. But in early 80s they noticed that few people that took that vaccine started to

develop chronic neurologic convulsions (epileptic fits), so they stop using that vaccine (the

cellular type). Then they noticed that prevalence of whooping cough cases started to increase

so they switch to the acellular type (the acellular part is the toxin of Bordetlla pertussis)vaccine instead, and then the number of cases dropped dramatically.

These are the mechanisms of burditella pertussis. The organism binds through the fimbria

and produces a toxin and the toxin damages the cell. So what we are going to do? we use the

vaccine and it'll produce antibodies and the antibodies are going to bind to the attachment

protein (the fimbria; the cellular part) preventing the bacteria from binding, so no damage is

going to take place OR some antibodies will arise against the toxin (the acellualr part) and

neutralize it. The bacteria have to bind first then it'll produce the toxin, so we can have

antibodies against the attachment proteins of the bacteria as well as against the toxin.

Vaccines against smallpox could be both live attenuated vaccines and killed vaccines. Figure

24.7: the yellow line represents levels of antibodies against small pox, and they are always

high, and the blue line represents protection against smallpox, which is so high. But if you look

at the red line which represents the levels of cytotoxic T-cells you'll find them low, and the

idea is that killed vaccines don't get stimulated through the cytosolic pathways. And now since

smallpox is eradicated, if you get exposed it is enough to take the inactivated vaccine which

will give the patient the appropriate levels of antibodies against the disease, and protection is

going to be high as well.

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Vaccination against smallpox is a debate that's going on among the world health

organizations whether to vaccinate or not to vaccinate following these biological terrors or

biological warfares that we have talked about, if you remember, last semester.

How organisms evade the immune response?

Microorganisms are so evasive; they have many ways to escape from our immune response and

these are some examples:

Small RNA viruses like the . HIV is the most error-prone RNA viruses, it has reverse

transcriptase and it has two copies. The reverse transcriptase keeps reading the two copies

back and forth, during that process it makes lots of mistakes, so every time you are going

to get a new strain. The most important part of the virus that changes a lot is the

attachment proteins, the GP120, and those when they change, every time you get

exposed to that virus you are going to have a primary immune response, which means no

memory cells, that’s why it is so difficult to make vaccines against the HIV.

And the same thing applies for the ; every five or six years the virus goes

through two mechanisms: one is known as the , and the other is the

.

Antigenic drift is a mutation of a single base pair that alters the hemagglutinin molecule,

so you will get a new strain, or a new variant.

Antigenic shift is when the gene of hemagglutinin has been completely changed. Why?Because the influenza viruses are segmented, they have seven to eight segments

depending on the subtype of the virus, and if two types of different antigenic structures

infect animals, you will get a mix of the segments and thus a new virus will emerge. So the

process of a primary immune response occurs and memory cells and so on.

Figure 24.9: If we are infected, for example, in 2001 with a strain, and the strain lasts

maybe for 1 year or two, so next time you are infected you are going to have antibodies

and those antibodies are going to neutralize the virus. Y3ni in the first year, we'll have

antibodies production, the next year you still have the same strain, so the virus will beneutralized and we won't have epidemic or pandemic. Then the four or five years after

that, the antigenic drift is going to take place and minor changes will take place on the

surface of the virus, but some antibodies still can neutralize the antigen while others can't,

so you can have here infection but not compared to those of the complete antigenic

shift.

In the antigenic shift the whole antigens of the surface are going to change, so no

antibodies are going to neutralize the virus, that's why we will have a pandemic all over

the world, like the H1N1 or the swine flu that we had, if you remember, 2 years ago.

This is because of the antigenic shift and the change which happens usually every 7 to 10years. So expect to have a pandemic on a continuous basis!

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And this is the price that we are paying for being mortal!! This is an interaction between us

and the environment, microorganisms and who competes to survive. And if you are weak

and can't develop any resistant mechanism, then you'll disappear, like the Dinosaurs that

couldn't really cope with the environment and so they have vanished and disappeared!! I

hope through this global warming that we are having right now that we will staycompeting for the next 50-100 years!! :-s

Larger viruses, like DNA viruses, have different mechanisms. We have talked about

; they suppress the production of MHC antigens, so they don’t represent

those to cytotoxic T-cells, thus the innate system is required to take control over these

viruses through the natural killer cells.

What is the difference between T cytotoxic cells and natural killer cells? One has memory

and the other does not have memory. Natural killer cells are the ones that lack the ability

to memorize former infections, so the immune response by the NKs is not efficient

compared to that by the T cytotoxic cells, but at least it has the ability to get rid of aninfection.

Bacteria of special structures, like mycobacterium tuberculosis. We said that

has waxes; like wax B and mycolic acid which resist the damage by phagocytic

cells, so they stay in our bodies for a longer period of time, and even the macrophages

cannot take those, so you need to activate the macrophages, thus activating the tumor

necrosis factor (TNF) and the interferon gamma in order to damage the cells infected with

the bacteria.

Bacteria that escape from the phagolysosome into the cytoplasm like

. Lesteria has the ability to penetrate the phagolysosome's membrane into

the cytoplasm, so they escape the respiratory burst and they can stay in our bodies for a

longer period of time.

Pathogens that have very thick capsules. We talked about encapsulated bacteria, which

interfere with phagocytosis, they cannot be phagocytosed, so they stay in our body for a

longer period of time, and the counter mechanisms of defense in our body are the

production of immunoglobulins against the capsule, as they help in phagocytosis and the

destruction of the pathogen. Encapsulated bacteria stimulate thymus- dependent

antigens, and in order to counter that, we use conjugated vaccines, to make memory cells

and for the antigens to become thymus-dependent.

Worms are so evasive in our body; they can cover their cells with self antigens so they

cannot be recognized as foreign antigens and thus staying in our body for a longer period

of time. are worms that can stay in our body for many years, but the problem

is not from the worm itself, it is from the eggs which produces and its body's secretions;

what comes out the eggs.

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Chapter 25

Hypersensitivity reactions

We said that we have successes in the immune system, like clearance of infection, making

vaccines, monoclonal antibodies… All of these are successes. And we have failure, and the

failure that we could have is the excessive production of immune products that are not

needed and these excessive products are not against the microorganism only, they could be

against environmental antigen where we should not respond against, so as a response our

tissue could be damaged.

are defined as reactions that occur because of hyper-stimulation of

our immune system; over-reactive immune system. Over-reactive means it has lots of

protection but on the other side we could have damage as well.

Around 10 -20% of all humans all over the world have one element of a hypersensitivity

reaction, and those are overprotected; they are less likely to be infected with microorganisms

and less likely to develop malignancy as well, so they live longer compared to ones that they

don't have hypersensitivity. But the other side of the story is that these hypersensitivity

reactions could kill as well! So it depends where the balance is going to be.

These excessive reactions that we have in our immune system could have so many factors that

involve; microorganisms could induce hypersensitivity reaction, like group A beta hemolytic

strep and these reactions against it damage our tissue, while it's supposed to react against the

microorganism itself, but it turns around and damages our cells. When we are infected with

influenza virus or common cold, we'll see lots of secretion; the mucus glands get infected,

running nose, this is a form of hypersensitivity reaction to these viruses. When we get infected

with mycobacterium tuberculosis, the damage that occurs to the lungs is a hypersensitivity

reaction. The damage that occurs to the liver when we get infected with hepatitis B virus,

when it turns into chronic, IFN gamma damages the cells (the hepatocytes) and not just that!

The virus is oncogenic; it can convert the cells into malignant and we could have

hepatocellular carcinoma.

Harmless environmental substances like pollens of flowers, and in our part of the world themost common harmless environmental substances that we are exposed to is the pollen of the

olives; many people are allergic to the pollens of the olive tree and the pollens antigens can

induce hypersensitivity reactions which could end up with rhinitis or what we used to call

, sneezing, coughing… At the time of the pollens production between the end of March,

April and early May, this is the time of the year where people are allergic. Some people are

allergic to dust, for example. Some mite excretions, fecal material of mites, and so on, which

people could be allergic too.

Some people could be allergic to self antigens; hypersensitivity reaction to a self antigen, this

is a form of autoimmune diseases.

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Using Coombs and Gell system and based on the types of immune response involved, we

classify the hypersensitivity reactions into 4 types:

we call it which involves an antigen that

stimulates IgE antibody production sensitizing mast cells then degranulation of those mast

cells and the secretion of vasoactive amines. It is the most rapid one; it acts within minutes.

when we have an antibody (IgM or IgG) reacts against an antigen on a surface of a

cell, so the antibody develops against that part of the cell, so complement will be activated

and the cell will be damaged. We call it .

when immune complexes develop. We have antigen-antibody reaction then

immune complexes develop and these immune complexes precipitate in tissues and then

complement will be activated and all what complement is going to bring into.

we call it . Occurs after 48-72 hours, like Mycobacterium

tuberculosis and contact dermatitis where macrophages and T-helper cells are going to be

involved and granuloma development as well.

Nour Rousan <3 from the first day and till this day; I just can't lose you! Thanks a lot for helping dear! :)

Dalia Rawashdeh <3 you are so thoughtful & so sincere; where it's difficult to find someone to be so…

Highly appreciate your help honey :)

Leen Shawaheen <3 How precious to have you! A sister of a lifetime…Thank you for helping sweets! :)

To Thurayya Huwwari <3<3<3 (You didn't help :P ;) I know you were ready to) thanks for being a part I

really love & pleased for of my life :)

To Raghad Al-Sheyyab <3 ta7eyyeh mn il 8alb :') & to ALL the beloved ones.

"I've learned that people will forget what you said, people will forget what you did, but people will

never forget how you made them feel" - Maya Angelou

… And that was it! :D

Bl-tawfee2 jamee3an

Dima M. Bani-Eisa

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