Combinatorial and junctional diversity of the immune system; isotype switching Flashcards
is there a B and T cell for every antigen out there?
yes
why must B and T cell antigen binding sites be explained by somatic cell recombination and not having a gene for each
if there was a gene for each, then the number of genes would exceed the number of genes in the human genome
describe B cell receptor structure
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
describe T cell receptor structure
alpha and beta chain, joined by DS bridge
constant and variable region; ABs at the end
what’s unique about how T cells recognise antigens
describe how T cells bind to antigens
need to be in the form of peptides attached to MHC markers
bind to both the peptide antigen and the MHC marker
describe helper T cells
CD4/8
what MHC marker
where is the MHC marker found
CD 4 class II marker; only found in antigen presenting cells
describe cytotoxic T cells
CD4/8
what MHC marker
where is the MHC marker found
CD 8
Class I marker; found on all nucleated cells
describe germline DNA structure
multiple V,D,J and coding segments
describe the variable region a bit more
has 3 hypervariable/complementarity determining regions, which form loops and come together to form antigen binding site
describe where hypervariable regions are found on beta/heavy and alpha/light
on all: CDR1/2 on V
on beta/heavy: CDR3 on VDJ
on alpha/light: CDR3 on VJ
which one of the VDJ “casettes” has the most variability and why
J
combinatorial diveristy and junctional diversity
describe recognition signal sequences in V D and J
5’ V-7-9
5’ 9-7-D-7-9
5’ 9-7-J
conserved heptamer and octamer; 12/23 linker in between
describe the process of recombination
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
when and where does recombination occurs
while B and T cells are developing, in bone marrow and thymus respecitvely.
when does junctional diversity occur
before ligation
what enzymes are involved in junctional diveristy
deoxynucleotidyl transferase adds nt
exonuclease removes nt
when does isotype switching occur
upon clonal selection
in general how does isotype switching occur
recombination of segments after VDJ, in response to helper T cell signals
what signal for what is shape of IgA IgD IgE IgG IgM
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
