B cell activation

Question 1

B-2 follicular cells

Answer 1

-re-circulating B cells: Majority

Question 2

B-2 marginal B cells

Answer 2

-reside in the spleen: blood-borne polysaccharide Ags

Question 3

B-1 cells

Answer 3

-mucosa-limited Ag specificty

Question 4

Migration of Naive B cells

Answer 4

1. passage through SLT, enter through HEV
2. No antigen, migrate to primary follicle (CXCR5)
3. recieve signal to survive (FDCs)
4. Exit through efferent lymphatic vessel competition for survival signals
5. naive B cells will die within weeks in absence of antigen

Question 5

First Signal of B cell activation

Answer 5

1. Ag recognition by mlgs
2. must crosslink 2 or more BCR
3. Ag with bound C3d recognized by mlgs and CR2 (Ag is now more immunogenic)
4. Syk-B cell phosphorylation

Question 6

Migration of Activated B cells

Answer 6

1. after activation by Ag in the follicular area, B cells change their chemokine receptor expression and migrate to the edge of the follicular zone
2. activated B cells secrete low levels of IgM and increase expression of co-stimulatory molecules and cytokine receptors

Question 7

T-dependent Immune Synapse

Answer 7

1. co-stimulatory signals are generated through the interactions of CD40:CD40L and adhesion molecules
2. Cytokine modulated class switching
3. Induced expression of activation-induced deaminase enzyme

Question 8

Somatic Hypermutation

Answer 8

10^3 to 10^4 times higher than normal spontaneous mutation rates

Question 9

Tfh

Answer 9

• CD4+, low levels of CD25 expression

- secrete IL-21

Question 10

T-independent Ag B cell activation

Answer 10

• B-1 cells respond to T-independent responses
• marginal zone B cells (B-2) in spleen recognize blood-borne polysaccharides
• Mainly igM, low-affinity antibodies, short-lived plasma cells

Question 11

Memory B cells

Answer 11

• survival for long periods of time without additional Ag stimulation
• express high levels of anti-apoptotic protein Bcl-2
• capable of mounting a rapid response to subsequent exposure to same Ag (secondary immune response)

Question 12

Antibody feedback

Answer 12

• control mechanism triggered by secreted Ab that blocks further Ab production
• IgG only, has ITIMS

Question 13

Humoral Immunity

Answer 13

• Branch of adaptive immunity mediated by antibodies produced by B cells and plasma cells
• principle defense against extracellular pathogens
• Abs are produced by plasma cells in the lymphoid tissues/organs
• effector function of Abs are mediated by the Fc region, all functions are triggered by the binding of Ag to the Fab (V) region

Question 14

Primary response

Answer 14

• within 5-10 days
• peak response is small
• mostly IgM
• mower average affinity

Question 15

Secondary response

Answer 15

• within 1-3 days
• Larger response
• increase in IgG, under certain situations, IgA or IgE (heavy chain isotype switching)
• higher average affinity

Question 16

Fc region

Answer 16

• Deliver antibody to inaccessible anatomical sites

- link bound antigen to molecules/cells that effect destruction

Question 17

Neutralization

Answer 17

• many microbes bind to the surface of cells to gain entry
• Ab neutralize the infectivity and potential effects of infection
• Abs may sterically hinder binding of microbes

Question 18

Opsonization and Phagocytosis

Answer 18

• Fc receptors on immune cell populations promote phagocytosis and deliver signals
  1. Opsonization of microbe by IgG
  2. Binding of opsonized microbes to phagocyte Fc receptors
  3. Fc receptor signals activate phagocyte
  4. phagocytosis of microbe

Question 19

ADCC (Antibody-dependent cellular toxicity)

Answer 19

• NK bind to antibody-coated cells by Fc receptors and destroy infected cell

Question 20

Natural Antibodies

Answer 20

• Mainly IgM, some IgG
• produced by B-1 and marginal zone B cells
• All blood group have IgG and IgM except for AB

Question 21

IgE mediated reactions

Answer 21

• IgE binds to Fcę receptors on present mast cells

- Ag binding causes degranulation of cell

Question 22

Neonatal immunity

Answer 22

• IgG from maternal circulation, FcRn transports it across placental barrier
• IgA secreted in breast milk

Question 23

Vaccination

Answer 23

• mimics a natural infection

- normal immune response is invoked to destroy and clear components of the vaccine

Question 24

Passive immunization

Answer 24

• immediate immunity but transient
• prevent disease after a known exposure
• protect immunosuppressed patients
• block action of bacterial toxins and prevent diseases that they cause
• Ex: snake bite anti-venom, passive transfer of Ig from mother to child