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15 Cards in this Set

  • Front
  • Back
Ag exposure leads to what 2 general processes?
Affinity maturation and Clonal selection
what changes occur after Ag exposure in regards to Ig production?
incr secreted: mbr-bound Ig ratio
somatic hypermutation
incr affinity of Ig for Ag
class switching
what is somatic hypermutation?
SHM: point mutations
occurs in ALL CDR REGIONS (v. only CDR3 in recombination)
where does SHM take place?
SHM occurs in 2ndary lymphoid follices; specifically GERMINAL CENTERS
where is SHM occurring with the greatest freq?
SHM occurs primarily near genes for the variable region
freq of SHM decreases as move away from V(D)J gene region
what are some consequences of SHM?
can incr or decr biding affinity;
have no effect
increase diversity
generation of stop codons, missense
what is clonal selection?
hypermutating B cells test new Igs on Ag-Ig complex on dendritic cells
incr affinity-> B cell received survival signal
decr affinity-> B cell dies
what happens with serial Ag exposure?
cont Ag exposure results in an incr in the freq of mutations in CDR 1 and 2!!
what is receptor revision?
if, after SHM, B cell reacts with self, has the option to change V region before being killed
what does isotype switching depend on?
cytokines rel by T cells
what does isotype switching involve?
translation of H chain C-region genes
"looping out" and loss of DNA
maintains specificity and affinity of V-region
incr fxnal diversity of Ig
what happens if an IgM-prod B cell does not receive signals from TH cells?
B cell will cont to express and secrete only IgM
what happens if B cell receives signals from TH cells?
recombination of switch regions
looping out of intervening DNA
--> Ig with new heavy chain C-region
what are switch regions?
areas of recombination between genes coding for diff Ig classes
NO switch region between IgM and IgD-->no IgD expression after Ag exposure
what occurs during post-transcriptional processing of primary mRNA for Ig?
remove introns and J gene segments
RNA splicing of exons
leader seq dir mRNA to ER for assembly