antibodies and B lymphocytes

Question 1

B lymphocyte origin

Answer 1

derived from stem cells in bone marrow; migrate into circulation (blood, lymphatics) and lymphoid tissue; mature B cells are specific for a particular antigen

Question 2

describe immunoglobulin gene rearrangement to form unique B cell receptors (BCR)

Answer 2

B cells encode a massive repertoire so produce many different antibody molecules with specific BCR: functional genes don’t exist until generated during lymphocyte development; each BCR chain encoded by separate multigene families on different chromosomes; when maturing, these gene segments are rearranged and brought together to form unique BCRs

Question 3

4 features of clonal selection

Answer 3

all lymphocytes have single, unique receptor; interaction between foreign antigen and receptor causes activation; differentiated effector cells of same lineage have same receptor; self-specific receptors deleted in early development

Question 4

what type of molecule is the BCR

Answer 4

surface bound Ig, encoding the antibody the cell will make

Question 5

when is the BCR created

Answer 5

during maturation before cell encounters antigen

Question 6

what does the BCR recognise

Answer 6

intact EC antigen

Question 7

what 3 components make up the transmembrane complex on the BCR

Answer 7

mIg (monomeric Ig), Ig-a and Ig-B

Question 8

what type of structure are Ig-a and Ig-B

Answer 8

heterodimers

Question 9

what do Ig-a and Ig-B heterodimers contain

Answer 9

Ig-fold structure

Question 10

which cytoplasmic tails contain ITAM and are long enough to interact with IC signalling molecules

Answer 10

Ig-a and Ig-B, as cytoplasmic tail of mIg is too short

Question 11

structure of BCR

Answer 11

diagram

Question 12

what 3 chromosomes are involved in coding for Ig chains

Answer 12

kappa light, lambda light, all heavy chains

Question 13

where are the genes coding for variable regions stored

Answer 13

upstream of constant regions so don’t have to repeat constant region DNA

Question 14

principles of Ig light chain expression

Answer 14

in germline DNA, 30-40 variable (V) regions encoded, followed by 5 joining (J) regions and a constant (C) region - found in immature B cells; as B-Cell develops, 2 V regions and 1 J region randomly selected alongside C region; alternative splicing patterns produce mature mRNA that has one V, J and C region that can be translated

Question 15

what does the Rag (recombination-activating gene) complex do in Ig light chain expression

Answer 15

encodes V(D)J recombinase and removes unused DNA

Question 16

principles of heavy chain rearrangement and expression

Answer 16

in germline DNA, 65 V regions, 27 D regions, 6 J regions and 9 constant region genes are encoded; same shuffling process occurs due to recombination as becomes B-Cell; mature B-Cells have 1 V, 1 D, 2 J and all 9 constant genes; primary transcript has VDJJ and constant regions for type of antigen present; alternative splicing further produces diversity in heavy chains

Question 17

1 difference between light and heavy chain expression

Answer 17

D region only in heavy

Question 18

disease caused by deficiency in Rag

Answer 18

SCID