Combinatorial and junctional diversity of the immune system; isotype switching

Question 1

is there a B and T cell for every antigen out there?

Answer 1

yes

Question 2

why must B and T cell antigen binding sites be explained by somatic cell recombination and not having a gene for each

Answer 2

if there was a gene for each, then the number of genes would exceed the number of genes in the human genome

Question 3

describe B cell receptor structure

Answer 3

2 heavy chains
2 light chains
each has constant and variable region
heavy chains joined by DS bridge
light/heavy chains joined by DS bridge
antigen binding site at the end

Question 4

describe T cell receptor structure

Answer 4

alpha and beta chain, joined by DS bridge

constant and variable region; ABs at the end

Question 5

what’s unique about how T cells recognise antigens

describe how T cells bind to antigens

Answer 5

need to be in the form of peptides attached to MHC markers

bind to both the peptide antigen and the MHC marker

Question 6

describe helper T cells
CD4/8
what MHC marker
where is the MHC marker found

Answer 6

CD 4
class II marker; only found in antigen presenting cells

Question 7

describe cytotoxic T cells
CD4/8
what MHC marker
where is the MHC marker found

Answer 7

CD 8

Class I marker; found on all nucleated cells

Question 8

describe germline DNA structure

Answer 8

multiple V,D,J and coding segments

Question 9

describe the variable region a bit more

Answer 9

has 3 hypervariable/complementarity determining regions, which form loops and come together to form antigen binding site

Question 10

describe where hypervariable regions are found on beta/heavy and alpha/light

Answer 10

on all: CDR1/2 on V
on beta/heavy: CDR3 on VDJ
on alpha/light: CDR3 on VJ

Question 11

which one of the VDJ “casettes” has the most variability and why

Answer 11

J

combinatorial diveristy and junctional diversity

Question 12

describe recognition signal sequences in V D and J

Answer 12

5’ V-7-9
5’ 9-7-D-7-9
5’ 9-7-J
conserved heptamer and octamer; 12/23 linker in between

Question 13

describe the process of recombination

Answer 13

recombination activating gene ensymes attach to the linkers.
enzymes attach, forming and excising loop (HOWEVER: remaining strands need to be 12/23 to enable VJ/VDJ)
other enzymes clean up overhangs
ligase joins VJ/VDJ to form coding join

Question 14

when and where does recombination occurs

Answer 14

while B and T cells are developing, in bone marrow and thymus respecitvely.

Question 15

when does junctional diversity occur

Answer 15

before ligation

Question 16

what enzymes are involved in junctional diveristy

Answer 16

deoxynucleotidyl transferase adds nt

exonuclease removes nt

Question 17

when does isotype switching occur

Answer 17

upon clonal selection

Question 18

in general how does isotype switching occur

Answer 18

recombination of segments after VDJ, in response to helper T cell signals

Question 19

what signal for 
what is shape of
IgA 
IgD
IgE
IgG
IgM

Answer 19

A - TGF-b (b after a); dimer
D - none; membrane attached
E - IL-4 (L looks like E); monomer
IgG - none; monomer
IgM - IFN-y (N after ; pentamer