c39 lec 5 and 5.5 and 4 Flashcards
how does mHC molecules have diversity
- polymorphisms:multiple variations, or allles of each gene within the population
- polygeny: many genes for MHC I and MHC II
- misaligned chromosomes
- NO SOMATIC RECOMBINATION AND NO GENE REARRANGEMENT
where do most polymorphisms/variation occur in MHC molecules
peptide pocket/peptide binding groove
MHC molecules only bind to peptides through
key anchor residues
- So MHC molecules are able to bind to a diverse range of peptides because they only need to recognize a little part/sequence called key anchor residues, they don’t need to recognize whole antigen
the combination of MHC alleles found on a single chromosomes
MHC haplotype
selection of heterozygotes/heterozygosity
balancing selection
do TCRs and BCRs undergo somatic gene rearrangment?
yes
is a soluble form of TCR secreted?
no, think T cells don’t produce antibodies, only B cells
how many polypeptides makes up TCRs and BCRs?
2 for TCRs
4 for BCRs (remember they have two arms)
what is a surrogate light chain
two proteins (with no recombinations) that mimic binding of light chain to heavy chain to see if it works
what is a pre BCR
when we check the functionality of rearranged heavy chain with surrogate light chain and it works, so therefore it passes the first checkpoint and now it can make a light chain
successful heavy chain rearrangement
a single B cell only expresses and rearranges one heavy chain to produce BCRs with two identical heavy chains
allelic exclusions
what restricts light chains in the number of attempts to rearrange the same gene
the number of J (joining) segments
ex. if there are 5 J segments then it has 5 opportunites to rearrrange properly which is contrast to heavy chains which only have one opportunity for rearrangement per gene segement (one opportunity per chromosome remember)
in negative selection when self-reactive B cells rearrange their light chain to produce a self-tolerant BCR
receptor editing
once an immature B cell is self-tolerant (able to not recognize self antigens), it leaves the bone marrow
central tolerance
immature B cells that fail to produce self-tolerant BCR undergo apoptosis
clonal deletion
- cell dies through negative selection! good
negative selection that continues outside of the bone marrow is called
peripheral tolerance
unresponsive to antigen
anergy
B cells that compete for space in this tissue become mature B cells.
positive selection
how many attempts to arrange a heavy chain and how many attempts to arrange a beta chain per gene copy
2 for heavy chain in B cells
4 for beta chain in T cells
mkae sure that proteins that are specific to not just the thymus but all throughout the body are expressed
AIRE (autoimmune regulator)
peripheral tolerance of T or B cells are a result of
anergy = unresponsive to antigen
happens through negative selection
