B cells and production of antibodies 2

Question 1

what are germinal centres

Answer 1

• specialised microstructures in secondary lymphoid tissue where B cells differentiate
• spleen, peyers patches and lymph nodes

Question 2

how are B cells activated by T cells

Answer 2

• b cells process antigen and display it to Tfh cells in complex with MHC class 2
• Tfh cells express CD40L and IL-21

Question 3

what does CD40L do

Answer 3

activates CD40 receptor on B cells

Question 4

what does IL-21 do

Answer 4

proliferation in plasma and memory cells by STAT3

Question 5

what do Tfh cells produce that regulates class switching

Answer 5

IL-4, IL-6, TGH beta and IFN-y

Question 6

what do thymus independent antigens do

Answer 6

allow B cell activation in the absence of Tfh cells
- activates NF-kB pathway

Question 7

what are centroblasts

Answer 7

rapidly dividing B cells that divide every 6-8 hours

Question 8

what do centroblasts express

Answer 8

CXCR4, CXCR5 but reduce IgD expression

Question 9

what do stromal cells express

Answer 9

CXCL12 to keep centrotoblasts in dark zone

Question 10

what is the dark zone

Answer 10

gene rearrangement events with signals from the light zone

Question 11

what makes up the majority of germinal centres

Answer 11

proliferating b cells

Question 12

what happens to germinal centres in dark zones

Answer 12

v chain rearrangement
- mutations change one to a few amino acids
- subtly different antigen specificities

Question 13

what do germinal centre b cells express

Answer 13

activation induced cytidine deaminase
- reduced antigen binding capacity causing apoptosis by negative selection

Question 14

describe the process of somatic hypermutation

Answer 14

• negative selection
• B cells have high antigen binding specificity
• AID induces somatic hypermutation
• new antigen binding specificty causes continued hypermutation
• reduced antigen binding specificity causes apoptosis

Question 15

describe the steps of apoptosis of B cells

Answer 15

• engulfment by tangible body macrophages
• regulation of cell, numbers in follicle preventing swelling

Question 16

what facilitates transition to light zone

Answer 16

• periodic expression of CXCR4

Question 17

what happens when there is a transition to the light zone

Answer 17

• b cells become centrocytes and encounter follicular dendritic cells
• bind MCH class 2 to check binding affinity
• high binding affinity reduces CXCR4 expression

Question 18

describe the positive selection of B cells

Answer 18

• when mutation improves binding specificity of receptor to antigen
• b cell has increased ability to acquire antigen
• increased antigen-MCH class 2 complexes on cell surface
• increases binding avidity of FDC to B cells