Antibodies And Antigens

Question 1

How many polypeptide chains are present in an antibody?

Answer 1

Four - two light and two heavy chains.

They are bound by disulfidige bridges and noncovalent interactions.

Question 2

What region of the antibody is responsible for antigen binding?

Answer 2

The variable region

Question 3

What is the Fab fragment?

Answer 3

Fragment Ag-binding

Question 4

Both the heavy and light chains are divided into V and C regions. What do the V and C regions contain?

Answer 4

The V region contains the Ag-binding site and the C region determines the fate of the Ag.

Question 5

What are the 5 different kinds of H-chains that determine the class of antibody?

Answer 5

Mew

Delta

Gamma

Sigma

Alpha

Question 6

What are the 5 different classes of antibodies?

Answer 6

M

E

A

D

G

Question 7

True or false: each Ab unit can have only a kappa or lambda L chain,b ut not both.

Answer 7

True

Question 8

What are some of the interactions betweenthe H and L chains?

Answer 8

Intrachain disulfide bridges.

They create polypeptide loops, domains, of 110 amino acids.

Question 9

What are the Ig superfamily proteins?

Answer 9

A large group of cell surface and soluble proteins that are involved in the recognition, binding or adhesion processes of cells.

Question 10

What are some members of the Ig superfamily?

Answer 10

IgG

CD4 receptor of T cells

CD28

ICAM-1

Question 11

The Ag-binding sites are formed by the juxtaposition of what two domains?

Answer 11

The VL and VH domains.

Question 12

A membrane bound IgM on a B cell has what?

Answer 12

C terminal transmembrane and cytoplasmic portions that anchor the molecule in the plasma membrane.

Question 13

What is IgG cleaved by?

Answer 13

Papain.

Question 14

What does papain digestion allow for?

Answer 14

The separation of two Fab fragments and complement-and Fc receptors binding the Fc fragment.

Question 15

What does pepsin generate?

Answer 15

A single bivalent antigen-binding fragment, F(ab’)

Question 16

What is the role of hinges in Abs?

Answer 16

It allows the antibodies to change how they spread their antigen binding sites.

Question 17

What is affinity?

Answer 17

The tightness of Ag-Ab binding.

Question 18

The higher the binding constant, the ___ likely the Ab is to dissociate from the Ag.

Answer 18

Lower

Question 19

Abs formed in the primary response soon after the injection of an Ag are generally ___ affinity.

Answer 19

Lower

Question 20

Abs produced by a memory response have ___ affinity than those in a primary respnose.

Answer 20

Higher

Question 21

When is an example of when affinity of an Ab is critical?

Answer 21

When the Ag is a toxin or virus and must be neutralized rapidly at low titers.

Question 22

What is valence?

Answer 22

The maximum number of antigenic determinants with which an Ab can react.

Question 23

IgG contains two Fab regions and can bind two molecules of Ag or two identical sites on the same particle. What is its valence?

Answer 23

2

Question 24

What is an advantage of having two or more binding sites for an Ag?

Answer 24

It can dramatically increase the tightness of binding of the Ab to Ags.

Question 25

What is avidity?

Answer 25

It gives a measure of the overall strength of an Ab-Ag complex. It is dependent on: Affinity of the Ab for the epitope Valence of both the Ab and the Ag

Question 26

low affinity IgM can be extremely effective in neutralizing a microorganism. Why is this so?

Answer 26

It has a large number of binding sites.

Question 27

When antibodies change from membrane to secreted form, how does their effector function change?

Answer 27

They change from a B cell receptor function to effector function.

Question 28

When antibodies undergo isotype switching, how is effector function changed?

Answer 28

Each isotype serves a different set of effector functions.

Question 29

When there is affinity maturation in the variable region of an antibody, how is antigen recognition changed?

Answer 29

There is increased affinity of antigen recognition.

Question 30

What are IgGs involved in?

Answer 30

Phagocytosis

Question 31

What are IgAs involved in?

Answer 31

Mucosal defenses

Question 32

What are IgEs involved in?

Answer 32

Allergic responses

Question 33

What are IgMs involved in?

Answer 33

Complement activation

Question 34

What is the most common Ab in mucosal secretions?

Answer 34

IgA

Question 35

What Ab is mainly found in the plasma?

Answer 35

IgM

Question 36

What Ab is found on the surface of mast cells?

Answer 36

IgE

Question 37

What Ab penetrates deep into the tissue?

Answer 37

IgG

Question 38

What is the most abundant Ig in the blood?

Answer 38

IgG

Question 39

What Ig provides the bulk of immunity to most bloodborne pathogens?

Answer 39

IgG

Question 40

What is the only Ab class that can cross the placenta to provide passive humoral immunity to the developing fetus and to the infant on its birth?

Answer 40

IgG

Question 41

What is the function of FCRn (receptor for Fc regions)?

Answer 41

It transfers maternal IgG to the fetal circulation. This will provide important protection prior to the generation of immunocompetence in the fetus.

Question 42

What is the primary function of IgD?

Answer 42

It is an Ag receptor on B lymphocytes and is also involved in regulating B cell function when it encounters Ag.

Question 43

Naive B cells can express what two Igs?

Answer 43

IgM and IgD. Both are specific for the same Ag.

Question 44

When IgM and IgD are expressed on a B cell, what happens to the Ag?

Answer 44

The Ag is internalized, processed and presented to helper T cells.

Question 45

What is the fate of Ag activated B cells?

Answer 45

They proliferate and differentiate into plasma cells, thus initiating the developmentof a humoral immune response.

Question 46

What is the first Ab produced by any Ag-activated B cell prior to contact with T helper cells?

Answer 46

IgM

Question 47

What is an important role of IgM?

Answer 47

It plays a critical role in defense before sufficient quantities of IgG have been synthesized.

Question 48

Where is IgM primarily found?

Answer 48

In the bloodstream

Question 49

The overall avidity of an IgM is ___, making IgM very effective in the removal of the microbe.

Answer 49

High

Question 50

What is the major Ig present in the colostrum, milk and saliva?

Answer 50

IgA

Question 51

What are two unique polypeptide chains of IgA?

Answer 51

Secretory component (SC) J-chain (joining chain) The SC component is responsible for stabilizing IgA against proteolytic degradation in the GI tract.

Question 52

How are the two Ig units comprising the secretory IgA held together?

Answer 52

By the J-chain through disulfide bridges.

Question 53

Which Ig is is a major defense mechaism against microbial invaders at mucosal surfaces?

Answer 53

IgA

Question 54

What Ig is present at low levels in the serum?

Answer 54

IgE

Question 55

What does IgE play a signficiant role in?

Answer 55

Enhancing acute inflammation, in protection from infection by worms and in allergic reactions.

Question 56

What type of cells does IgE bind to?

Answer 56

Receptors on mast cells.

Question 57

What are effector properties of Abs?

Answer 57

Immunomodulation Direct antibacterial activity Toxin neutralization Activation of complement Opsonization Organized T-cell response Reduced damage to host from inflammatory response