W02_B Cells

Question 1

recall the clonal selection theory

Answer 1

lymphocytes develop based on need - only those whose receptors are stimulated continue proliferating to produce clones that target that antigen

Question 2

what are the 3 functions of antibodies?

Answer 2

neutralization, opsonization, complement activation

Question 3

why can’t IgM be an opsonin?

Answer 3

there is no IgM Fc receptor on phagocytes, so IgM is solely for activating complement

Question 4

what is IgA best for?

Answer 4

neutralization. it’s no good at opsonizing and activating complement

Question 5

where is IgE found?

Answer 5

Fc bound to surfaces of mast cells. antigen binding at Fab region causes degranulation

Question 6

what is the order of somatic recombination in the chains?

Answer 6

heavy: D+J, +V, +C;
light: V+J, +C

Question 7

how do pre-B cells progress?

Answer 7

first heavy chain selected, then light chain (kappa then lambda). if failed, then apoptosis. immature B cell makes IgM

Question 8

what is B cell tolerance?

Answer 8

B cells need to be selected against self-antigens. they develop self-restriction, or tolerance. this is central tolerance in the bone marrow.

Question 9

how do b cells home?

Answer 9

enter lymph nodes through high endothelial venules

Question 10

what comprises the B cell co-receptor?

Answer 10

CD19, CR2, CD81

Question 11

what do b cells do to get T cell help?

Answer 11

once bound to the antigen, they express CD40, which binds to CD40L on the Tfh cell. Tfh cell secretes cytokines to B cell

Question 12

where is the primary focus of activated B cells?

Answer 12

medullary chords of lymph nodes

Question 13

what types of Ab do B cells make in the primary foci?

Answer 13

IgM; no help from T cells

Question 14

where is the germinal center (secondary focus)?

Answer 14

between B cell and T cell zones; IgG made here

Question 15

what’s in the germinal centers?

Answer 15

activated B cells, helper T cells, follicular dendritic cells (not immune cells)

Question 16

what happens in the germinal centres?

Answer 16

somatic hypermutation + affinity maturation. as the epitope regions become more specific, B cells can bind to T cells better, and get more signals to survive. thus, only the best and most specific B cells will survive to make antibodies

Question 17

what is isotype switching?

Answer 17

changing the Fc region to become IgG, IgA, or IgE (from IgM). occurs as recombination of the cluster of C genes after VDJ

Question 18

which cytokine turns B cells into plasma cells?

Answer 18

IL-10

Question 19

which cytokine turns B cells into memory B cells?

Answer 19

IL-4

Question 20

note: plasma cells are terminally differentiated, and will not change any longer. they also have short lifespans

Answer 20

okay.

Question 21

where are plasma cells found?

Answer 21

bone marrow.

Question 22

what are BAFF and APRIL?

Answer 22

B cell activation and survival factors; note that excess BAFF can have high Ab production, and anti-BAFF can treat lupus

Question 23

note: child gets IgG through placenta while still in womb, and IgA through breast milk to coat gastric mucosa post natal

Answer 23

okay.

Question 24

how do RBCs help to clear immune complexes?

Answer 24

they have CR1 receptors on their surface to pick up antigen, and deliver to spleen and liver, where macrophages pluck immune complexes off the RBCs.

Question 25

which antibody do you test for in acute infection? in chronic infection?

Answer 25

IgM for acute. IgG for chronic.

Question 26

what is goodpasture’s syndrome?

Answer 26

antibodies directed against the basement membrane of kidneys

Question 27

what can C3 and C4 levels in the patient tell us?

Answer 27

low levels may indicate immune complex disease with complement consumption

Question 28

where are memory B cells?

Answer 28

in bone marrow or circulation