Antibody structure, B cell diversity, B cell development

Question 1

B cell receptors are referred to as

Answer 1

Immunoglobulins

Question 2

Soluble forms of B cell receptors are

Answer 2

Antibodies

Question 3

BCR chains

Answer 3

Polypeptides are folded into separate domains, each with a separate function
- domain: compact and rigid structure held together by noncovalent bonds

Question 4

Light chain

Answer 4

Single variable domain and a single constant domain

Question 5

Heavy chain

Answer 5

Single variable domain and 3-4 constant domains

Question 6

Variable region

Answer 6

Antigen recognition!!

- all antibodies differ in the number and types of amino acids encoded in the variable region

Question 7

Constant region

Answer 7

Determines effector function of the antibody

- recognized by leukocytes and plasma proteins

Question 8

The constant region is also known as the ____

Answer 8

Fc region

Question 9

How many classes of antibodies are there and what are they defined as?

Answer 9

5 classes called isotopes. Defined by heavy chain constant region
- IgG, IgA, IgM, IgD, IgE

Question 10

Isotope

Answer 10

Member of related gene family

• heavy chain with different effector functions
• differ in domains and amino acid contents (varies with affected body parts and how pathogen is to be eliminated)

Question 11

Different effector functions of antibodies are directed by _____

Answer 11

Heavy chain constant region

Question 12

____ is the first antibody produced in a primary immune response

Answer 12

IgM

Question 13

Isotope switching

Answer 13

Later in the immune response different isotypes are produced

- heavy chain variable region of IgM along with original light chain is expressed with a different heavy chain isotype

Question 14

B cell receptor recognizes the _____

Answer 14

Native form of an antigen

- important because the antibody will link the pathogen to the leukocytes and plasma proteins that will eliminate it

Question 15

Epitope

Answer 15

Part of the antigen bound by the antibody

• antibodies recognize epitopes on a protein or carb antigen
• epitope can be a cluster of amino acids or portion of a polysaccharide

Question 16

The ____ of the antigen-binding site must be ____ to the shape of the epitope

Answer 16

Shape; complementary
- heavy and light chains pair to form a variety of shapes that can accommodate a variety of different antigen epitopes (1 specific shape per antibody)

Question 17

Cross reactivity

Answer 17

An antibody generated against one antigen that binds to an unrelated antigen

• shared
• similar

Question 18

Shared epitope

Answer 18

Different antigens share the same epitope (basis for vaccines)

Question 19

Similar epitope

Answer 19

Some pathogens express protein or carbohydrate epitopes that resemble host epitopes

Question 20

Monoclonal antibodies

Answer 20

Antibody originating from a single B cell

• the antibody is specific for one epitope
• used frequently for diagnostics (ex: heartworm test)

Question 21

Polyclonal antibodies

Answer 21

A mixture of antibodies, each specific for a different epitope from the same antigen

Question 22

Somatic recombination

Answer 22

DNA recombination that occurs between gene segments in the immunoglobulin genes
- takes place during B cell development in the bone marrow

Question 23

How does the process of somatic recombination contribute to the diversity of antigen-binding sites?

Answer 23

There are multiple copies of gene segments in the light chain gene and the heavy chain gene = amplification of diversity

Question 24

Construction of the antigen-binding site by somatic recombination

Answer 24

• Gene segments are used to construct variable region of light and heavy chain gene
• Gene segments differ from one another in short regions (hypervariable regions)
• Process of somatic recombination results in random addition of nucleotides at the joints between gene segments –> responsible for diversity of HV3

Question 25

Somatic recombination variable region

Answer 25

Antigen binding site differs from one antibody to the next because of differences in the number and kinds of amino acids encoded in the 3 HV regions

Question 26

Control tolerance

Answer 26

Removal of immature B cells with specificity for self-proteins (autoreactivity)
- only B cells tolerant to self proteins present in the bone marrow will be exported into the blood

Question 27

Surveillance

Answer 27

Naive B cells exported to the periphery circulate through secondary lymphoid tissues

Question 28

Mature naive B cells

Answer 28

The same variable region domain is expressed with 2 different heavy chains (IgM and IgD)
- both isotypes served as an antigen receptor

Question 29

Primary immune response

Answer 29

• Recognition of antigen
• Activation by helper T cells
• Differentiation to short-lived plasma cells producing IgM
• Surface expression of IgM and IgD is downregulated as activated B cells differentiate to short lived plasma cells

Question 30

Why is IgM secreted as a pentamer in a primary immune response?

Answer 30

IgM generally possesses low affinity for the antigen epitope –> pentameric structure increases the valence from 2 antigen binding sites to 10 antigen binding sites
- increases affinity, less likely to dissociate, and provides a binding site for C1q