Blk 3 Flashcards
(39 cards)
what are the two types of selection of alpha/beta Tcells in thymus
Positive selection and negative selection
what can CD8 tcell recognize?
MHC1
what happens to the cells that survive positive selection?
move to medulla of thymus for negative selection
what happens to tcells that bind with too high of affinity to mhc?
die
most important part of negative selection
tcells are exposed to AIRE gene product in the medulla of the thymus.
what does the exposure of tcells to AIRE gene products allow for
allows epithelial cells that express theses genes to turn on tissue restricted genes
what is the relevance of the tcells to be exposed to AIRE gene products in the medulla of the thymus
the AIRE gene expresses genes from all over the body, this allows the tcells to be tested against self reaction to many parts of the body at the same place. the ones that are reactive to these genes are killed.
in negative selection, why isnt only the thymus protected against self reacting Thymocytes?
because in the medulla of the thymus the AIRE product gene is expressed, which expresses genes from all over the body.
why TCRs dont undergo somatic hypermutation?
because unlike BCR which does somatic hypermutation, TCRs need to remain specific to a particular MHC molecule.
thymic education
positive and negative selection.
what are the 2 types of TCRs?
alpha/beta (95%). and gamma/delta (5%)
what are the structures that form a TCR?
1 heterodimers (alpha/beta, or gamma/delta) 2 Ig family domains 3 transmembrane region 4 short cytoplasmic transduction tails 5 C terminus constant region 6 N terminus variable domain that contain Complementary Determining Regions (CDRs) CDR1, 2, 3,
where are CDR1 and CDR2 encoded
in the same V gene segments
how is CDR3 generated?
it is generated during joining of the segments, this makes it by far the most diverse segment
how is CDR3 generated?
it is generated during joining of the segments, this makes it by far the most diverse segment
how are the interactions vary btw different CDRs?
CDR 1 and CDR2 make contact with the shoulder of the MHC molecules and CDR3 with the antigen peptide
there are about 10^7 TCRs on a given Tcell, how do they differ?
they do not differ. they are exactly the same due to alellic exclusion after a successful chain is made
how do the binding with antigen differ btw Bcells and Tcells in terms of affinity for the peptide?
Bcells binds with several orders of magnitude more than Tcells to antigens
what is the signigicance of the weak interaction btw TCRs and antigens?
they will need co-receptors CD4 and CD8 to help hold the cells together during signal transmission
what is the reason for CD4 to bind to MHC2 and CD8 to MHC 1?
the co-receptors. CD4 binds to beta invatient region of MHC 1, and CD8 binds alpha chain of alpha invarient region of MHC1
where do tcell receptors concentrate their diversity?
in the 3rd hyperviable region. CD3
where CD1 and CD2 bind to?
to the MHC
TCR gene rearrangements results in what?
diversity within CDR 1, 2, and 3
when is the alpha locus rearranged?
after the beta locus is good
