Immunoglobulins

Question 1

What are the different heavy chains of an antibody?

Answer 1

μ, γ, α, β, ε

Question 2

What are the different light chains of an antibody?

Answer 2

κ, λ

Question 3

What determines the specificity of the immunoglobulin?

Answer 3

Complementary Determining Regions (CDRs)

Question 4

Why might we need Ab diversity?

Answer 4

Recognize Ag of pathogens

Question 5

How is diversity of Ab achieved?

Answer 5

Somatic Recombination (VDJ)

Question 6

What is the process of VDJ recombination?

Answer 6

1. Stem cell (Germline DNA)
2. Progenitor B cell - heavy chain rearrangment
3. Precursor B cell - light chain rearrangement
4. Immature B cell
5. Mature B cell (VDJ rearranged DNA)

Question 7

How many VDJ gene segments does the heavy chain contain?

Answer 7

Variable - 40
Diversity - 25
Joining - 6

Question 8

How many VDJ gene segments does the light chain (λ) contain?

Answer 8

V - 30
D - N/A
J - 4

Question 9

How many VDJ gene segments does the light chain (κ) contain?

Answer 9

V - 40
J - 5

Question 10

How is the variable region formed?

Answer 10

1. Germline DNA goes through somatic recombination to form D-J joined rearranged DNA
2. D-J joined rearranged DNA goes through somatic recombination to form V-J or V-DJ joined rearranged DNA
3. Then goes through transcription to form primary transcript RNA
4. Splicing of RNA occurs to form mRNA
5. mRNA undergoes translation to form polypeptide chain

Question 11

What is the structure of a recombination signal sequence?

Answer 11

Heptamer - 7 bp
Spacer - 12 or 23 bp
Nonamer - 9 bp

Question 12

What is the usual heptamer sequence?

Answer 12

CACAGTG

Question 13

What is the usual nonamer sequence?

Answer 13

ACAAAAACC

Question 14

What are the names of the two mechanisms used to make a recombination signal sequence?

Answer 14

1. Hairpin loop
2. Tangled configuration

Question 15

What determines the classes of Ig?

Answer 15

Isotypes of heavy chain constant (CH) regions determine the classes of immunoglobulin, which are differentiated by large structural and functional differences.

Question 16

What are the characteristics of IgM?

Answer 16

1. 5-10% of the immunoglobulin pool
2. Confined to intravascular space
3. Additional component involved in multimerization

Question 17

What are the functions of IgM?

Answer 17

1. Primary immune response
2. Activation of complement

Question 18

What are the characteristics of IgG?

Answer 18

1. 70-85% of the Ig pool
2. Longest half life (20-24 days)
3. Four subclasses - 1, 2, 3, 4

Question 19

What are the functions of IgG?

Answer 19

1. Secondary immune response
2. Activation of complement pathway
3. Binds to macrophages and neutrophils for enhanced opsonization
4. Can cross placenta and can enter fetal circulation

Question 20

What are the characteristics of IgA?

Answer 20

1. 5-15% of Ig pool
2. Predominant in mucous secretions
3. Two subclasses - 1, 2

Question 21

What are the functions of IgA?

Answer 21

1. Transport across epithelial cells
2. Activation of complement pathway
3. Binds to macrophages and neutrophils for enhanced opsonization
4. Gut protection

Question 22

What are the characteristics of IgE?

Answer 22

1. Low abundance
2. Additional constant domains

Question 23

What are the functions of IgE?

Answer 23

1. Immunity to parasites
2. Allergic reactions
3. Binds to basophils and mast cells

Question 24

What are the characteristics of IgD?

Answer 24

1. Less than 1% of Ig pool
2. Located on B-cells

Question 25

What are the functions of IgD?

Answer 25

1. Unknown function
2. May play a role in eliminating B cells