4- Immunoglobulin Structure

Question 1

What are the classes of imunoglobulins?

Answer 1

Ig(G, A, M, D, E)

Question 2

Characteristics of IgG

Answer 2

Predominant Ab induced in secondary response.

Crosses human placenta due to presence of FcRn

Question 3

Characteristics of IgA

Answer 3

Predominant Ig in external secretions

Occurs as a dimer

Does not cross placenta

Key role in mucosal immunity

Question 4

Characteristics of IgM

Answer 4

Predominant Ab induced in primary response.

Pentameric in its secreted form

Does not cross placenta

Expressed on surface of B-cells as monomer

Question 5

Characteristics of IgD

Answer 5

Found mainly on surface of B cells

Question 6

Characteristics of IgE

Answer 6

Involvement in Allergic Hypersensitivities

IgE Ab(s) fix to mast cells and basophils via an Fc receptor on the cells.

Question 7

What is the determinate of an Ig isotype?

Answer 7

The heavy chain

Question 8

The 2 classes of antibody light chains.

Answer 8

Kappa and Lambda

Question 9

General function of J-chain

Answer 9

Joining of Ig subunits

Question 10

Cross-linking of IgE on mast cells (via allergen) leads to…

Answer 10

degranulation of the mast cells

Question 11

3 methods by which antibodies mediate humoral immunity

Answer 11

(1) neutralization: antibody binding prevents bacterial adherence and permeation
(2) Opsonization: antibody directly promotes phagocytosis (because all phagocytic cells have Fc receptors [FcR])
(3) Complement activation: antibody activates complement, which enhances opsonization and lyses some bacteria

Question 12

What accounts for immune protection at birth? At what points do the antibodies reach adult levels?

Answer 12

The neonate is protected by passively transferred maternal IgG for the first few months after birth. Adult levels of IgM are reached at about 10 months of age; IgG at 4 years; IgA at about 10 years of age.

Question 13

Monoclonal vs Polyclonal antibodies and associated therapies

Answer 13

Mono –> all bind the same antibodies (ex. tumor specific antibodies)

Poly –> bind different types of antibodies (ex. IVIG for treatment of inflammatory diseases)

Single B-cell types make single antibodies (monoclonal). A combination of these gives you polyclonal antibodies.

Question 14

What gene segment is unique to the H chain?

Answer 14

Diversity (D) segments

Question 15

Order of Ig gene rearrangement and B cell development.

Answer 15

(1) Heavy chain-DJ rearrangement
(2) Heavy chain- VDJ rearrangement
(3) Light chain- VJ rearrangment

Question 16

What is unique about Heavy Chain-VDJ rearrangement?

Answer 16

This only occurs in cells committed to become B lymphocytes and is a critical control point in Ig expression because only the rearranged V gene is subsequently transcribed.

Question 17

Monoclonal vs Polyclonal antibodies and associated therapies

Answer 17

Mono –> all bind the same antigens (ex. tumor specific antibodies)

Poly –> bind different types of antigens (ex. IVIG for treatment of inflammatory diseases)

Single B-cell types make single antibodies (monoclonal). A combination of these gives you polyclonal antibodies.