lecture 21/22 - b cell responses

Question 1

What initiates B cell activation?

Answer 1

Antigen BCR binding via membrane immunoglobins→ Complex taken up into the cell→ presentation of antigen to T helper cells → activates B cell which then proliferates and differentiates into plasma and memory cells

Question 2

Describe the general phases of the B-cell mediated response

Answer 2

Antigen recognition → activation of B lymphocytes → clonal expansion and differentiation→
→ effector celles w antibody secretign plasma cells → antibody secretion
→ IGG expressing B cell → isotype switching
→ affinity maturation→ mature B cell

Question 3

Compare and contrast the primary and secondary antibody response

Answer 3

Primary : responding cell is naive
Primary antivy response from those that make IgM
Lag response
Low Ab concentration and affinity
Class switching to IgG under cytokin influence from helper cells

Secondary: responding cell is memory
No lag phase
Higher affinity and antibodies
Mostly IgG

Question 4

What is the recognition phase?

Answer 4

Ab recognition → expression of effector molecules by T cell → B cell activation →
Proliferation
Differentiation to testing memory cells and antibody secreting plasma cells

Question 5

Describe the 3 different signalling systems for B cell activation, how do they compare?

Answer 5

1
Ag binding to membrane Ab
Igalpha-Igbeta induces cascade to increase expression in MHCII and B7
Complex internalized by endocytosis → antigen degradation nd presentation on MHC II
Cell recognizes Ag via B7 CD28 costim signal to activate Th cells and induce CD40L on Th cell
2
Once CD40/CD40L interaction occurs
Nf-kb factor activation → cytokine receptor expression on B cell
3
B cell proliferation and differentation

Question 6

Describe the mechanism for cytokine secretion

Answer 6

Helper T adheres to B cells → IL4 and CD40 ligand → Helper T reorients cytoskeleton and secretory apparatus towards B cell → cytokine release close to point of contact → IL-4 release and confined ot space between B cell and T cell

Question 7

Which antibody doesn’t undergo affinity maturation

Answer 7

IGM and IGD bc they can undergo class switching

Question 8

What controls class switching?

Answer 8

The AID enzyme

Question 9

How do thymus dependent and independent antigens compare?

Answer 9

Independent→ B cell activation doesn’t rely on CD4 T cell help
Usually non protein antigens
Dependent → b cell activation in response to antigen requires CD4 T cell help

Question 9

How do thymus dependent and independent antigens compare?

Answer 9

Independent→ B cell activation doesn’t rely on CD4 T cell help
Usually non protein antigens
Dependent → b cell activation in response to antigen requires CD4 T cell help

Question 10

T1 vs. T2 independent antigens

Answer 10

1: antigen binds mitogen receptor and potentially BCR, inducing mainly IgM with no memory response
2: antigen cross-links BCRs, class switching can occur and some memory B cells can be formed