Immuno Learning Objectives

8/2/2019 Immuno Learning Objectives

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Learning Objectives

Introduction to Immunology

Please define

Antigen

Substance which canbe recognized by the immune system.

Antigenic Determinant

Part of the antigen that fits into the receptor, which is recognized by the immune system.

Toll-Like Receptor (TLR)

Participating protein class in innate immunity, these proteins recognize non-human

molecular structures. When bound to foreign particles, they induce a signaling cascade to

stimulate inflammation.

Pattern-Recognition Receptor (PRR)

Proteins expressed by cells of the innate immune system to recognize foreign molecular

structures known as pathogen-associated molecular patterns (PAMP).

Pathogen-Associated Molecular Pattern (PRR)

Foreign molecular structures that are recognized by TLRs or PRRs.

Cytokine

Factors synthesized by the PAMP-stimulated cell.

Chemokine

Factors synthesized by the PAMP-stimulated cell.

Discuss the role of the innate immune system.The role of the innate immune system is to recognize molecular signales or motifs and to

respond and act based on these recognized signals. It recognizes PAMP, DAMP, and the

absence of “self” markers.

Describe how innate immunity can lead to adaptive immunity,

and name the cell that bridges the two systems.If the innate response cannot handle the infection, then adaptive immune system is needed.

Immature phagocytic cells known as dendritic cells (DC) get activated by cytokines and

chemokines, and indiscriminately engulf foreign antigens. Activated dendritic cells leave the

local area and travel (through the lymphatic system) to the nearest lymph node, where they

present antigen-presenting cells. This allows development of an adaptive immune response.

Give an example each of how the immune system can be helpful

or harmful to its host.

Helpful

The immune system can be helpful by stopping infections that are present in the immune

system. The human body can respond well to a second infection without actually repeating

the whole series of infection.





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3. Others diffuse away from the site where antibody is interacting with antigen, and

attract phagocytic cells.

Define the concept of immunopathology, and give two

examples.Immunopathology is the branch of medicine that deals with immune responses to disease.There are four common mechanisms of immunopathology:

Mechanism Definition Cause Example

Type I

Immunopathology

Immediate

hypersensitivity to

pathogens

Too much IgE to respond to environmental

antigen

Allergies, Asthma,

Anaphylactic Shock

Type II

immunopathology

Autoimmunity due

to antibodies

(Reaction against

self.

Foreign antigens look like self, causing a cross

reaction with self. Based on normal antibody

immunity. Antibody binds, complement is

activated, phagocytes areattracted, and they

attempt to eat the antigens.

Graft v. Host,

Transfusion reaction

Type III

immunopathology

When an antibody

is made against a

soluble antigen.

Immune complexes of antigen and antibody are

usually eaten by phagocytes, but are too small,

and may get trapped in the basement membrane

of capillaries they circulate through. Happens

where there is a net outwar movement of fluidfrom blood to tissues. The trapped complexes

activate complement and the inflammatory

response occurs.

Arthritis, Systemic

Lupus

Erythematosus

Type IV

immunopathology

T cell mediated

(autoimmune)

T cells attack body cells due to the presence of

foreign antigens.

Tuberculosis or

Acute Viral Hepatitis

AIDS Immunodeficiency

by a virus, namely

human

immunodeficiency

virus.

The AIDS virus, HIV-1, infects Th cells because

its envelope glycoprotein, gp120, binds to the

CD4 cmolecules they have on their surface.

Inside it uses its enzymes (reverse ranscriptase,

to copy its RNA into DNA which becomes

inserted into the cell’s own DNA.

HIV

Anatomy and Physiology of the Immune System

Define:

Leukocytes

Nucleated cells of the blood; white blood cells.

Mononuclear Cells

Leukocytes whose nucleus has a smooth outline. Examples: Monocytes and Lymphocytes.

Polymorphonuclear Cells

Cells whose nucleus is lobulated, also called granulocytes because they have (usually) rather

prominent cytoplasmic granules. Exmaples: Eosinophils, Neutrophils, and Basophils.

Granulocytes

Cells that contain prominent cytoplasmic granules. Found typically in polymorphonuclear

cells.

Mast Cells

Cell in recognizing tissues that contain histamin and heparin granules. Most prominent in

hypersensitivity responses such as allergy and anaphylaxis.



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Plasma and Serum

Plasma is the yellow component of blood, which suspends blood cells, composing of 55% of the

total blood volume. It contains fibrinogen, and contains dissolved proteins, glucose, clotting

factors, ions, hormones, and carbon dioxide. Blood serum is plasma without the fibrinogen or

clotting factors.

Sketch schematically a neutrophil; eosinophil; basophil; smalllymphocyte; lymphoblast; plasma cell; monocyte. Indicate the

characteristic features which distinguish each cell type.Cell Sketch Characteristic Features

Neutrophil - Multilobulated nuclei.

- Colorless granules.

Eosinophil - Multi-lobulated nuclei.

- Red granules

Basophil - Multi-lobulated nuclei

- Blue granules

SmallLymphocyte

- Cytoplasmic “halo”- Large nucleus

- Single nucleus



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Lymphoblast - Presence of Golgi

Apparatus

- Multiple nucleoli

Plasma Cell - Presence of Rough

Endoplasmic Reticulum

- Three nucleoli

Monocyte - U-shaped nucleus

- Large size

Define antigen, and compare it to immunogen. Discuss a

potential use, if any, antigen could be made into a tolerogen. Antigen is a substance that induces an immune response. An immunogen is an antigen,

which can give rise to an immune response, that is, which can immunize a host. Not every

antigen is an immunogen. Potential uses to antigen that can be made into tolerogens is thedesensitization of pollen or even a faster recovery rate in organ transplantation. Tolerogens

do not generate an immune response. Creating antigens that do not spur an immune

response allow the body to function properly without the side effects associated with an

immune response.



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Discuss lymphocyte activation by antigen with respect to:

receptor binding, proliferation, and differentiation.

Antibody Structure

DefineH (Heavy) chain

Chain of polypeptides that has a molecular weight of ~50,000.

L (Light) chain

Chain of polypeptides that has a molecular weight of ~25,000.

Kappa and lambda chains

Types of L chains. Remain the same during change of H chains.

Hinge region

Proline-rich portion of an immunoglobulin heavy chain between the Fc and Fab regions that

confers mobility on the two Fab arms of the antibody molecule, allowing it to combine betterwith two epitopes.

Fab, F(ab’)2, Fc

Fab (fragment antigen-binding: region on an antibody that binds to antigens.

F(ab’)2 (fragment antigen binding, divalent): divalent fragments that contain two light

chains and two variable region heavy chains.

Fc (fragment, crystallizable): Complement-fixing domain (tail-region) that interacts with Fc

receptors of the complement system. Utilized to activate the immune system.

Complementarity-determining region

Regions within immunoglobulins where proteins interact with antigens. Determine the

protein’s affinity and specificity for antigens.

Variable V and constant C regions

Variable V region: Sequence between antibodies of different specificities. Comprises the

antibody’s combining site, which binds antigen.

Constant C region: Region that is essentially identical, no matter what the specificities of the

antibodies are. Made up of 1 (in L chains) to 4 (in epsilon and mu) compact, structurally-

similar domains.

VL and CL

VL: Variable domain in light chain

Receptor Binding

• Lymphocytes have receptors.T cells have alpha and betachains. B cells have samples

of antibodies that the cellwill secrete. Antigen partthat fits onto the receptor isthe epitope.

• To activate the T or B cell:

• Fit between receptor andantigen is good enough(several receptors bound byantigen)

• For T cells, other cellsurface molecules must beinvolved.

Proliferation

• T cells and B cells because todivide and produce daughtercells.

Differentiation

• Lymphocytes mature andspecialize, becominglymphoblasts.

• T lymphocytes become Tlymphoblasts.

• B lymphocytes become Blymphoblasts, which turninto plasma cells.



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CL: Constant domain in light chain

Name the 5 antibody classes, and their characteristic heavy

chains.Clas

s

Norm.

Value

(mg/dL)

Diagram Charact

eristic

HeavyChains

Molecular

Weight

Function

IgG 1000 2 Light

and 2

Gamma

Chains

150,000 Main antibody in

blood and tissue

fluids. It neutralizes

toxins, binds bacteria

and facilitates their

destruction by

activating complement

and by binding them

to phagocytic cells.

IgE 0.02 2 Light

and 2

Epsilon

Chains

190,000 (an

extra

constant

domain, CH4,

and 18%

carbohydrate)

Dimer form in

secretions, where

secretory component

protects it from

proteolysis.

IgD 5 2 Light

and 2

Delta

Chains

180,000 (an

extra-long

hinge region)

First antibody to

appear in the serum

after immunization,

and it is very efficient

at activating

complement. IT does

not get into tissue

fluids very efficiently.

IgA 200 4 Light,

4 Alpha,

1 J, and

1 S.C.

chain

Secreted form

400,000

(monomer is

160,000; J

chain is

15,000 and

Secretory

Component is70,000)

Functions mainly as a

receptor on B cells.

IgM 100 10 light,

10 mu,

and 1 J

chain

900,000 (5 x

180,000; an

extra CH4

domain plus a

J chain)

Antibody which causes

Type I

immunopathology. It

is also called

immediate

hypersensitivity or

allergy. Also

important in

resistance to

parasites.

S.C.

J

J



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Draw a diagram of the structure of typical molecules of each

class. Label the heavy and light chains; Fc and Fab parts; J

chains; antibody combining sites; main interchain disulfide

bonds; secretory component.

Typical antibody molecule.

Class Diagram

IgG

IgE

IgD

IgA S.C.

J



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IgM

Discuss the significance of the fact that in any antibody

molecule, both H and both L chains are identical.Both H and both L chains are identical in order to maintain rotational symmetry and to

maintain its structure. This also allows multiple binding sites to be present in an antibody.

Describe the structure of antibody combining sites.When an IgG or IgM binds to at least one of its binding sites there is an obvious change in

the angle. IT becomes Y or T shaped!

1. BINDING/RECOGNITION Binding to phagocytic cells, especially PMNs,

eosinophils, and macrophages, which have receptors (FcR) for the altered Fc of IgG

but not of IgM.

2. PERFORMANCE OF FUNCTION C1q, first component of complement system,

binds to two adjacent Fcs and is activated.

J

Y

Y

Ab

C



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Explain why complementarity-determining regions are also

called hypervariable regions.

Complementarity-determining regions (CDR) are called hypervariable regions because of

variability along 3 areas of the V domain, and not distributed uniformly. These

hypervariable regions comprise of the actual antigen-binding site.

Give an example of a subclass, an allotype, an idiotype.

Subclass

IgG1, IgG2, IgG3, IgG4

IgA1, IgA2

IgM1, IgM2

IgD

IgE

Allotype

Gm (heavy chain) and km (light chain)

Idiotype

VL and VH in an antibody.

Define Fc receptors. Name the inflammatory cells that have

them.Fc receptors are receptors with a protein that stimulate phagocytic or cytotoxic cells to

destroy microbes, or infected cells in antibody-mediated immunity.

Receptor name Principal

antibody ligand

Affinity for

ligand Cell distribution

Effect following binding

to antibody

FcγRI (CD64) IgG1 and IgG3High (Kd ~

10−9 M)

MacrophagesNeutrophils

Eosinophils

Dendritic cells

PhagocytosisCell activation

Activation of respiratory

burst

Induction of microbe killing

FcγRIIA (CD32) IgG Low (Kd > 10−7 M)

Macrophages

Neutrophils

Eosinophils

Platelets

Langerhans cells

Phagocytosis

Degranulation (eosinophils)

FcγRIIB1 (CD32) IgG Low (Kd > 10−7 M) B Cells No phagocytosis

CDR

CDR

epitope

VH

VL

CL

CH1

CH2

CH3

hinge

CDR

CDR

epitope

VH

VL

CL

CH1

CH2

CH3

hinge



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Mast cells Inhibition of cell activity

FcγRIIB2 (CD32) IgG Low (Kd > 10−7 M)

Macrophages

Neutrophils

Eosinophils

Phagocytosis

Inhibition of cell activity

FcγRIIIA

(CD16a) IgG Low (Kd > 10−6 M)

NK cells

Macrophages (certain

tissues)

Induction of antibody-

dependent cell-mediated

cytotoxicity (ADCC)

Induction of cytokine

release by macrophages

FcγRIIIB

(CD16b) IgG Low (Kd > 10−6 M)

Eosinophils

Macrophages

Neutrophils

Mast cells

Follicular dendritic

cells

Induction of microbe killing

FcεRI IgEHigh (Kd ~

10−10 M)

Mast cells

Eosinophils

Basophils

Langerhans cells

Degranulation

Antibody Specificity, Diversity, Genes

Define

Toxoid

Bacterial toxin that has been weakened or suppressed by chemical or heat, while the

immunogenicity is maintained. Often used in vaccines, to induce an immune response to the

toxin or increase the response to another antigen.

DNA recombination

Changing the relative positions of two pieces of DNA.

RNA splicing

Modification of RNA after transcription.

Somatic hypermutation

Mechanism for immune system adaptation after encountering foreign microbes.

Define cross-reactivity. Give an example of a non-self antigen

which cross-reacts with a self antigen. Explain, in terms of

lymphocyte activation, how a self antigen might not itself elicit

antibody, but might react with antibody elicited by a cross-

reacting antigen.Cross-reactivity is the tendency of one antibody to react with more than one antigen, or a

reaction between the antibody and antigen that differs from the immunogen. It has to dowith goodness of fit. What happens is that it is against an antigen if it was immunized or in

a react with the antigen with a high association constant. This allows the adaptive immune

response to respond to toxoids and immune itself to toxins. This is the reasoning behind

vaccinations and immunizations, as the exposure to a toxoid (the harmless) allows resistance

to the toxin (the not-so-harmless).

Discuss the Clonal Selection Theory.Model of how the immune system responds to infection. It states that:



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- The immune system (B and T cells) is programmed to make only one antibody

- The choice of which antibody the cell will make is random, not dependent on outside

information.

- Entire population preexists in a normal individual, even before any contact with

antigens.

- When a new antigen is introduced into the body, it comes into contact with a huge

number of lymphocytes.- When it encounters one to whose receptors it binds with sufficient affinity, it

activates it, resulting in expansion of that clone and production of that antibody.

In short, the best-fitting clones are selected by antigen.

Define allotypic exclusion. Demonstrate your knowledge of the

concept by first stating the number of chromosomes in a cell

which bear H or L genes, and then the number that actually

contribute to a particular B cell’s antibody product. Allotypic exclusion is the process by which only one heavy chain (maternal or paternal) and

one light chain (kappa or lambda) is synthesized by an individual B cell, regardless of its

potential to make two different heavy chains and four different light chains.

Draw a diagram of the heavy and light chain gene regions of

human DNA. Indicate V, D, J and C subregions. Show how a

heavy or light chain gene is assembled out of these subregions

during the differentiation of a B cell.Start:

1 2 3 4 5 6 7...n 1 2 3...n 1 2 3...n µ ! " 1 " 2 # $ ...

D JV C

V region



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In heavy chains, basically:

1. Developing B cell first brings randomly one D segment close to one J. The DNA is

cut, the intervening DNA is excited and the ends joined.

2. The V segment is brought to the recombined DJ, and repeats the cutting and joining

process.

3. The entire region from the assembled VDJ unit through the end of the delta (of IgD)

constant region gene is then transcribed into nuclear RNA.

4. The primary RNA transcripts are alternatively processed by splicing, first to make

only VDJ-Cmu, and later to make both VDJ-Cmu and VDJ-Cdelta messages.

In light chains, basically:

The rearrangement is similar, but there are only V and J segments, no D, and only one C

domain gene.

Describe the somatic recombination model, which explains how

antibodies of the same specificity (idiotype) can be found in two

or more different classes (“class switching”).The somatic recombination model is a model of diversity generation by utilizing randomizing

mechanisms. It first utilizes exonucleases to remove a few nucleotides after the DNA is cut

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D is brought to

J; one random D is joinedto one random J; theintervening DNA is

excised

Then V is brought to D-J;one V is joined to the D-Jpair; the intervening

DNA is excised

A primary RNA transcript is made, from just left of thechosen V all the way throughto the right of the delta

constant region gene

The primary transcript RNA isalternatively spliced to make

VDJµ or VDJ! messages; the

cell makes IgM and, later, IgDtoo.

This is thegerm-line

situation1 2 3 4 5 6 7...n 1 2 3...n 1 2 3...n µ ! " 1 " 2 # $ ...

D JV C



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but before two gene segments (D to J, and V to DJ) are joined. Afterwards, it adds a few,

random nucleotides to the N region by utilizing an enzyme called terminal deoxynucleotidyl

transferase (TdT). This will cause a frame-shift mutation, and can cause termination of

transcription.

The change in the transcription leads to a change in mRNA. This is class switching is due to

the DNA mutation, from which a change from VDJ-mu can create VDJ-alpha, VDJ-gamma,or VDJ-epsilon. However, it cannot return to VDJ-mu because the frameshift mutation

caused removal of the mu functions. It can be found in two or more different classes (causing

class switching) by randomly mutating production of the mu, delta, alpha, or epsilon genes.

Define somatic mutation, and describe the essential difference

between the somatic mutation and germ line hypotheses of

immunological diversity.Somatic mutation is the theory that during embryonic lymphoid development, the genes

underwent repeated (somatic) mutation until a full complement of antibodies was produced,

and that not many V genes were in the germ line. This differed from the germ line theory,

which stated that the V genes were in the germ line, and that in the fertilized ovum, one

could predict all potential antibodies that an individual would have.

Describe the mechanisms by which more diversity is created by

nucleotide insertion and removal during V(D)J recombination.Mechanism B Cell Details T Cell Details

2-chain receptors

(combinatorial

diversity)

Each chain provides

half the receptor’s

CDRs

Heavys times lights Each chain provides

half the receptor’s

CDRs

Alphas times Betas

Recombination of

germ-line segments

(combinatorial

diversity) RAG-1

and RAG-2

H chains: 65 V, 27

D, 6 J = 10,500

combinations

L chains:

35 V, no D, 5 J = 175

10,500 times 175 =

about 2 million

antibodies

Beta chains:

50 V, 2 D, 13 J =

1,300 combos

alpha chains:

70 V, no D, 60 J =

4,200 combos

4,200 times 1,300 =

about 5.5 million T

cells

“Optional diversity” B cell can choosekappa or lambda L

chains

Roughly doublesnumber of

antibodies

There are also Tcells with

gamma/delta

receptors

Perhaps 5% of Tcells are

gamma/delta

N region diversity

(somatic)

Random nucleotides

added or subtracted

at VD and DJ joins

Estimated to

produce 100 times

more diversity than

the germ line

Random nucleotides

added or subtracted

at VD and DJ joins

Estimated to

produce 10,000

times more diversity

than the germ line

Somatic

hypermutation

After exposure to

antigen

Mutation rate is

about 1 in 104 cell

divisions

Does not occur

Total diversity

(including somatic

hypermutation

~1014 antibodies possible; many fewer

actually found in blood

~1011 TCR (T cell receptors) possible; about

108 found in blood

Antibody Function and Complement

Define:

Valence

Number of components of an antigen molecule to which an antibody molecule can bind. An

expression of the number of antigen-binding sites for one molecule of any given antibody or

the number of antibody-binding sites for any given antigen.



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Affinity

Attraction between an antigen and an antibody.

Precipitation

Moplecules react with antibodies, become insoluble, and fall out of solution.

Agglutination

Cells react with antibodies, become insoluble, and fall out of solution.

Distinguish the five classes of immunoglobulins in terms of:

Passage across the placenta, ability to activate complement by

the classical pathway, ability to activate complementby the

alternative pathway, involvement in allergic diseases, “First

line of defense”, most resistant to enzymatic digestionClass Passage

across the

placenta

Ability to

activate

complement by

the classical

pathway

Ability to

activate

complement by

the alternative

pathway

Involvement in

allergic

diseases

“First line

of

defense”

Most

resistant to

enzymatic

digestion

IgM No. Yes. No. No. Yes. No.

IgG Yes. Yes. No. No. No. No.

IgD No. No. No. No. No. No.

IgA No. No. Yes. No. Yes. Yes.

IgE No. No. No. Yes. No. No.

Compare and contrast precipitation and agglutination in terms

of the nature of the antigens involved, and sensitivity of the

tests.Precipitation Agglutinations

Antigens Involved Molecules Cells

Sensitivity of the Tests Less readily detected/Less sensitive More readily detected/More sensitive

Discuss how complement plays roles in both innate and

adaptive immunity.Complement has three different pathways: the classical, the alternative, and the lectin. The

classical is spurred by complexes of IgG or IgM antibodies with the antigen. It causes a 1-4-

2-3-5-6-7-8-9 C pathway, and it involved in adaptive immunity. The alternative is activated

by IgA-complexes and by cell wall structures, because the presence of certain cell wall

structures (dextrans, endotoxins) may also allow alternative to occur, so this would be innate

and adaptive. The lectin pathway is solely innate, because is is mediated by mannose-

binding protein, a lectin that attacks carbohydrates.



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List the components of complement in the order in which they

become activated in the classical pathway. Name those that are

also activated in the alternative pathway.

Classical Pathway: C1, C4, C2, C3, C5, C6, C7, C8, C9

Alternative Pathway: C3, C5, C6, C7, C8, C9

Discuss the lectin-mediated pathway of complement activation.The lectin-mediated pathway is mainly part of innate immunity. It is mediated by mannose-

binding protein, MBP or MBL, a lectin (proteins that bind to foreign carbohydrates. MBP

binds certain mannose-containing structures found in carbohydrates of bacteria but not

humans. MBP is functionally similar to C1q in the classical complement pathway.

Associating with MBP when it binds mannose are some serine proteases (MASPs) that

activate C2 and C4 and continue the cascade.

Discuss the different ways in which complement is activated

by: IgG; IgM; IgA; polysaccharides. Antibody/Molecule Pathway Type of

Immunity

How Complement is Activated

IgG Classical Adaptive Two IgGs close together binds to Fc portions of

antibodies after interaction with antigen, causing

changes in Fc portions and allows binding and

activation of C1q.

IgM Classical Adaptive Single IgM binds to Fc portions of of antibodies

after interaction with antigen, causing changes in

Fc portions and allows binding and activation of

C1q.

IgA Alternative Innate or

Adaptive

Presence of IgA-antigen complexes or cell wall

structures of foreign microorganisms, such as

dextrans, levans, zymosan, or endotoxin.

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MASP-1

MASP-2



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Polysaccharides Lectin Innate Use of mannose-binding protein (MBP) to target

mannose-containing structures in carbohydrates

of bacteria, but not in humans.

Identify the complement components which are: opsonizing;

lytic; anaphylatoxic; and chemotactic.Components C1 C2 C3 C4 C5 C6 C7 C8 C9

Opsonizing No No Yes

(C3b)

No No No No No No

Lytic No No No No Yes Yes Yes Yes Yes

Anaphlatoxic No No Yes

(C3a)

Yes

(C4a)

Yes

(C5a)

No No No No

Chemotactic No No No No Yes

(C5a)

No No No No

Ontogeny, T and B Cells

Define:

Stem Cell

Cells that can differentiate into specialized cell types and renew themselves to produce more

stem cells.

B Cell

Main cell involved in humoral immune response. The principal function of B cells is to make

antibodies, present as antigen-presenting cells, and develop into memory cells after

encountering antigens.

T Cell

Main cell in cell-mediated immunity.

Pre-B Cell

Precursor to development of B cells.

Pre-T Cell

Precursor to development ot T cells.

Self-tolerance

Process by which immune system does not attack self-antigens.



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Describe the sequence of appearance of cytoplasmic and

surface immunoglobulins in developing B cells. Using these

data, derive a model that could explain self-tolerance at the B

cell level (“clonal abortion”).

Basically, the “pro-B cell” is basically a progenitor cell with only a mu chain. When

cytoplasmic IgM is produced, with kappa or lambda chains, a pre-B cell is developed. As

soon as a surface antibody emerges (sIgM), then it becomes an immature B cell. Finally a

mature B cell emerges when surface IgM and surface IgD emerges.

Draw a graph showing the antibody response to a typical

antigen in a primary and in a secondary response. Show both

IgM and IgG antibody levels.

Basically, IgM is typically the major player in primary antibody response. In secondary

response, IgG is the major actor in secondary antibody response, with the help of helper T

cells.

Draw a graph, which shows relative IgG and IgM levels in a

normal infant from conception to one year of age. Distinguish

maternal from infant’s antibodies.



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Mother’s IgG is the primary antibody for the fetus, as it is able to pass through the human

placenta.

Given a newborn’s antibody titer, interpret its significance if

the antibody is IgG, or IgM. If IgG, calculate what the titer will

be at 4 months of age, and state the assumptions you madewhen you did the calculation.

The significance of whether the antibody is IgG or IgM is the rate of production of each

antibody. Infant IgG is not produced until 3 months after birth. However, IgM is produced

since approximately 3 months post-conception. Maternal IgG allows the fetus’s immune

system to be maintained.

T Cells 1 and 2

List the four main types of T cells, and define their functions.Type of T Cell Surface

Marker

Helper or

Killer

Functions

Th1 (delayed

hypersensitivity)

CD4 Helper - Secretion of lymphokines (interferon gamma/INF-gamma) when

encountering an antigen.- IFN-gamma is pro-inflammatory, being chemotactic for blood

monocytes and tissue macrophages, and causes stimulation of

phagocytes.

Th17 CD4 Helper - Makes inflammatory lymphokine IL-17.

- Resembles Th1 in that its main job seems to be causing

inflammation.

Th2 CD4 Helper

Tfh (follicular

helper)

CD4 Helper

Treg CD4 Helper

CTL CD8 Killer

Describe the surface markers that can be used to distinguishbetween T and B cells in humans.Cell Type Surface Markers

B sIgD, sIgM

T CD3, CD4, CD8



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Describe markers that Th1, Th2, and killer T cell (CTL)

subpopulations in humans have on their surfaces.T Cell Markers

Th1 CD3, CD4

Th2 CD3, CD4

CTL CD3, CD8

Define lymphokine and cytokine, and give an example of each.Name Definition Example

Cytokines Short-range mediators made by any cell, that affect the behavior of

the same or another cell

IL-1, TNF-alpha, IL-12

Lymphokines Short-range mediators made by lymphocytes, that affect the behavior

of the same or another cell. A subset of cytokines.

IL-2, IFN-gamma, IL-4,

IL-5, IL-109

Chemokines Small (6-14 kD) short-range mediators made by any cell, that

primarily cause inflammation.

MIP-1 to MIP-4,

RANTES, CCL28,

CXCL16, Eotaxin, IL-8

Describe an activity of interferon-gamma.Interferon-gamma is a lymphokine that is the main activator for monocytes and

macrophages. What it does is activate the macrophages to M1, where it becomes involved inaggressively ingesting bacteria and foreign pathogens, causing also releasing of

macrophages’ cytokines to intensify inflammation.

Define mitogen, and name two T cell mitogens. Name a mitogen

that stimulates both B and T cells in humans.Mitogen is a T cell mitosis stimulant. Basically, it promotes cell division of T cells. Two

examples of mitogens are phytohemagglutinin (PHA) and concanavalin A (Con A). A

mitogen that stimulates both B and T cells in humans is known as pokeweed mitogen

(PWM).

Distinguish between the effects of a mitogen and an antigen

when added to normal blood lymphocytes.Protein Effect

Mitogen Triggers cell division in lymphocytes

Antigen Triggers production of antibodies.

Compare and contrast the antigen receptors of T and B cells.

Cells Antigen Receptors

T - Structurally reminiscent of antibody two chains are called alpha and beta and has a common

mplementarity-determining regions.

%

% %



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and variable portion.

- T cell makes its receptor out of V (D) and J regions recombined as in B cells and like antibody.

- Each chain has 3 CDRs2; the process takes place in the thymus.

- Both alpha and beta chains have transmembrane domains, unlike surface Ig, in which only the

heavy chains are transmembrane.

B - Consist of a ligand binding moiety and a signal transduction moiety.

- T Cell Receptor may have an evolved ancestor with B cell receptors, as structure is similar.

Discuss the structures recognized by T cell receptors.

Distinguish between what is recognized by helper and

cytotoxic T cells.

T cell receptors typically recognize major histocompatibility complexes (MHC I or II).

Major Histocompatibility

Complex

Recognizing Cells

I + Antigen CTL

II + Antigen Th1, Th17, Tfh, Treg, Th2

Discuss what is meant by “MHC-restriction”. Name the classes

of MHC molecules by which CTL, Th1 and Th2 are restricted.MHC restriction involves not seeing antigen alone, but only antigen presented to them on the

surface of a genetically-identical cell. The T cell and the antigen-presenting cell must come

from individals who share alleles at a group of genetic loci coding for surface glycoprotein

molecles.

Major Histocompatibility

Complex

Recognizing Cells

I CTL

II Th1, Th17, Tfh, Treg, Th2

Class I products are on all nucleated cells, while Class II are presented on the surfaces of

dendritic and macrophage-type cells.



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Describe the role of T cells in ridding the body of a viral

infection.

1. Antigen enters body, causing innate response, and dendritic cell ingests breakdown

products.

2. Within the endosome, viral proteins are broken down by products.

3. Endosome fuses with other vesicles which have MHC molecules embedded in their

membrane, facing in. Some of the peptides associate with the MHC molecules.

4. Endosome recycles to the cell’s surface and fuses to the plasma membrane, thusexposing MHC molecules bearing antigenic peptides to the outside world.

CREATION OF ANTIGEN-PRESENTING CELLS.

5. T cells receptors recognize APCs and induce immune response, because T cells only

see antigen when complexed with surface MHC molecules, because it also does not

recognize free antigen.

Describe the characteristics of T-independent antigens.Major

Characteristic

Description

Composition Molecules with the same, repeated epitope. Found commonly in complex carboydrates.

Response Almost all IgM, need T cell help to convert to IgG, IgA, or IgE.

Discuss the mechanism by which T cells help B cells.

Observations

1. T cell and B cell must come from donors with the same MHC Class II.

2. T ell and B cell need not be specific for the same epitope, but the epitopes they arespecific for must both be on the same antigen molecule.

3. If you poison the B cell’s ability to endocytose it cannot be helped by a T cell or make

antibody.

Process

!"#

$%#&''

()#%#'*++%,,

*-./0&-

Antigen enters body,causing innateresponse, and

dendritic cell ingestsbreakdown products.

Within theendosome, viral

proteins are broken

down by products.

Endosome fuseswith other vesicleswhich have MHC

molecules embeddedin their membrane,facing in. Some of

the peptidesassociate with the

MHC molecules.

Endosome recyclesto the cell’s surface

and fuses to the

plasma membrane,thus exposing MHCmolecules bearing

antigenic peptides tothe outside world.

à CREATION OF ANTIGEN-

PRESENTINGCELLS.

T cells receptorsrecognize APCs and

induce immune

response, because Tcells only seeantigen when

complexed withsurface MHC

molecules, becauseit also does not

recognize freeantigen.



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1. B Cell binds the epitope on a foreign molecule that its receptor is specific for.

2. IT then endocytoses the bound molecule, and breaks it down in the endocytic vesicle.

3. Peptide fragments bind to MHC Class II molecules brought in by other vesicles that

fuse with the endosome, and then move to the surface.

4. Tfh sees epitope + Class II on the B cell’s surface.

5. Tfh binds to epitope and class II and focuses surface interactions and helper

lymphokines on the B cell.

a. Epitope does not have to be the same as the one the B cell saw.

Immunity and Vaccines

Compare the roles of cell-mediated and humoral immunity in

virus infections with regard to: preventing the infection;

controlling spread of viruses in the body; which is responsible

for recovery from disease; how each can cause

immunopathology.Type of Immunity Cell-Mediated Humoral

Preventing the Infection X

Controlling the Spread of

Virus in the body

X

Which is responsible for

recovery from disease

X

How each can cause

immunopathology

Viruses which never appear in the blood or

lymph, or go latent and express few proteins

are very hard to deal with.

Lack of antibodies caiuses viruses to

infect cells or kill them.

Inferences on the immune system:

1. Local immunity on the surface that is being invaded can prevent the invesion

secretory IgA. good levels of antibody indicates that patient is probably not

susceptible that virus.

Y

Th2B cell

MHC class II

antigen

Y

Th2B cell

MHC class IIY

Th2B cell

MHC class II

antigen

Tfh

BCellDisplayofAntigen+ClassII

BindingofTfHtoBCell



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Discuss the possible roles of Th1 and CTL in recovery from

virus infection.Cell Roles

Th1 - Presented by the dendritic cell on MHC II by.

CTL - Presented by dendritic cell on MHC I.

Define “local immunity” and give an example.Local immunity is innate or acquired immunity limited to a certain organ or tissue.

Examples include the Peyer’s patches in the small intestine, the appendix in the large

intestine or the tonsils.

Identify those organisms against which cell-mediated immunity

is most effective.Cell-mediated immunity is most effective against:

- Bacteria

- Intracellular bacteria

- Viruses (recovery from viruses)

Identifythoseorganismsagainstwhichhumoralimmunityismosteffective.- Parasites (IgE)

- Prevention of viruses

Identify the types of organisms against which IgE immunity

may play an important role; discuss possible mechanisms.- Parasites

Mechanisms:

- Worms produce a weak innate response, but there may be an uncharacterized

pattern recognition receptor that responds to their “parasite-ness” and strong

stimulates a Th2/Tfh response.

-

Production of IgG and IgEo IgG binds, activated complement, and C3a and C5a attract neutrophils.

o Neutrophils seize opsonized worm. Neutrophils lack helminthocidal

mechanism.

o Worm sheds antigens that diffuse to nearby mast cells loaded with anti-

helminth IgE.

o IgE is cross-linked by the antigens and the mast cells degranulate.

o Histamine causes gut smooth muscle contraction and violent peristalsis can

help expel worms.

o Late-Phase response prostaglandins and leukotrienes are elaborated

ECF-A they attract eosinophils in large numbers.

Eosinophils have Fc receptors for IgG eosinophils releases Major

Basic Protein toxic to helminthes.

Describe the mechanism by which trypanosomes in sleeping

sickness evade the host’s humoral immune response.Trypanosomes evade humoral response by extensive antigenic variation of parasite surface

glycoproteins known as major variant surface glycoprotein, contributing to its virulence.



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Give an example of a human and an animal antitoxin; a toxoid;

a killed virus vaccine; and a live virus vaccine. Identify the one

which produces the longest-lasting immunity. Discuss possible

hazards of each type of preparation.Type of Vaccine Definition Examples Produces longest-

lasting immunty

Hazards of each preparation

Human Antitoxin Use of human serum Tetanus

Immune

Globulin

Not enough to distribute for high

demand.

Animal Antitoxin Use of animal serum Horse

antitoxin

Readily causes serum sickness.

Toxoid Inactivated toxin Tetanus

toxoid

X The dirtier the vaccine, the more

likely unpleasant side effects

occur.

Evolved infectious agents can

evade immune response to toxoid.

Killed Virus Vaccine Preparations by

which killed agents

(whole) are

introduced.

Former

pertussis

and

typhoid

vaccines

Live preparations provide better

immunity than do killed

preparations.

The dirtier the vaccine the morelikely unpleasant side effects

occur.

Live Virus Vaccine Preparation by

which live agents

(attenuated to

removed disease but

still be antigenic)

are introduced

Smallpox

vaccine

Possiblility of infection and death

from the vaccine (administration

of the organism)

State the appropriate times for immunization of children

against diphtheria, pertussis (whooping cough), tetanus, polio,

and measles. Discuss why live viral vaccines tend to be

ineffective in the very young.Age0-6

Vaccine! Age" Birth

1month

2months

4months

6months

12months

15months

18months

19–23months

2–3years

4–6years

1 HepB

2 RV RV RV2

3 DTaP DTaP DTaP seefootnote3

Haemophilus in uenzae4 Hib Hib Hib4

5 PCV PCV PCV

6 IPV IPV

7

8 see footnote8

9

see footnote

9

10

11

HepBHepB

DTaP DTaP

Hib

IPVIPV

MMR

VaricellaVaricella

MMR

PCV

HepA Series

MCV4

Inuenza (Yearly)

PPSV

HepA (2 doses)



Age7-18

WhylivevaccinestendtobeveryineffectiveintheveryyoungChildren in their first year or two of life are poor at T-independent antibody responses, thus

conjugate vaccines are used (because the carbohydrate is coupled to a protein carrier so Tfh

cells could respond and focus help on the B cells).

Discuss the use of IgG and IgM antibody titers in the diagnosis

of intrauterine and neonatal infections.Titers are the reciprocal of the maximal dilution of a patient’s serum that is still positive in

some defined test. This is important because intrauterine and neonatal infections can cause

fetal abnormalities, and cause congenital malformations. Infection in utero causes

production of IgM in response to the disease, and its determination will allow indication of

congenital infection.

Identify the oral and parenteral polio vaccines by the names of

their developers. Discuss their relative advantages and

disadvantages, and note which is currently used in the USA.Type of

Vaccine

Definition Developers Advantages Disadvantages

Oral Administration

through

mouth.

Sabin

Long-lasting immunity,

prevention of reinfection of the

digestive tract, and lower cost.

More stable and less likely to

freeze.

Cannot be used for

patients with

compromised immune

systems because it still

live.

Parenteral Administration

through vein,

artery, bone, or

muscle)

Salk Immunity for

immunocompromised

individuals and can use dead

agents for vaccination.

Expensive, less table,

and more likely to

freeze.

Discuss the pros and cons and advances in pertussis (whoopingcough) immunization.In 1940, before the production of the vaccine, there were 250,000 cases with 7,000 deaths,

and there is no protection in herd immunity. When it first came out, it did prevent pertussis,

but it caused febrile states and brain damage in 1 per 310,000 doses. Now, it has been

replaced with acellular vaccines, which is ten times safer. However, one must take into

account that the bacteria can also evolve, and such evolution may reduce the effectiveness of

the vaccine.

Vaccine! Age" 7–10 years 11–12 years 13–18 years

Tetanus, Diphtheria, Pertussis1

Human Papillomavirus2 see footnote 2

Meningococcal3

Inuenza4

Pneumococcal5

Hepatitis A6

Hepatitis B7

Inactivated Poliovirus8

Measles, Mumps, Rubella9

Varicella10

Tdap

HPV (3 doses)(females)

MCV4MCV4

Tdap

HPV series

MCV4

Inuenza (Yearly)

Pneumococcal

HepA Series

Hep B Series

IPV Series

MMR Series

Varicella Series

Range ofrecommendedages forcatch-upimmunization

Range ofrecommendedages for allchildren

Range ofrecommendedages for certainhigh-risk groups

Documents

Immuno Learning Objectives