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