Lecture 7 - B Cell Developement

Question 1

Stages of B cell development

Answer 1

GENERATIVE LYMPHOID ORGANS
1. B Cells develop from pluripotent stem cells in the bone marrow.
2. The stem cell develops into a mature IgM+ B cell

PERIPHERAL LYMPHOID ORGANS
3. The mature, naïve B cells circulates through the peripheral lymphoid organs.
4. B cells that fail to encounter antigen die through apoptosis

PERIPHERAL LYMPHOID ORGANS
5. B cells that encounter antigen (1st signal) and receive a second signal are activated.

Question 2

Ig Heavy Chain Loci

Answer 2

3 loci called VDJ: consists of a variable (V) region of gene segments followed by a diversity (D) and joining (J) region of gene segments

Question 3

Ig Light Chain Loci

Answer 3

2 loci called κ and λ: variable and joining segments

Question 4

Stages of B Cell Activation

Answer 4

1. Naïve B cell encounters antigen.
2. Helper T cells stimulate B cells.
3. Activated B cells begin clonal expansion.
4. Some B cells differentiate into antibody secreting plasma cells.
5. Others become memory cells
6. Others switch class to produce a new Ig Isotype

Question 5

Memory Lymphocytes

Answer 5

Produced from naïve lymphocytes as a result of antigen exposure. Persist for years in a quiescent state. Rapidly reactivated by repeat exposure to antigen and mediate faster, more potent immune responses

Question 6

Secondary Versus Primary Antibody Responses

Answer 6

Secondary responses are more effective at dealing with infections. They’re faster, stronger, and more specific

Question 7

Class Switching

Answer 7

Changing of an antibodies constant region

A clone of B cells is not committed to make a single Ig isotype forever, but can switch to others.

**Class switching does not affect variable region
new constant region = new effector functions

— All mature B cells start out making IgM.
— Cytokine signals induce rearrangements at the heavy chain locus
— Exposed DNA ends are joined together, and DNA encoding some constant regions is deleted
— End result: New class of Ig