B Cell Life after Split with T Cell

For Immunology Chapter 12 Day 2

1. Activated B cells depart from their interaction with T cells at the T cell/B cell boundary and head either to the extrafollicular area to immediately begin developing into plasma cells or to the germinal centers (GC) where they go on to interact with FDC and T_FH. Explain which activated B cell fate produces either the soluble IgM or the soluble IgG during the primary response (see first half of figure 12-16).  Why do they make the Ab isotypes?
2. Draw a GC with a surrounding follicular mantle. What cell type(s) would be expected in the mantle, the dark zone of the GC, and the light zone of the GC.  Compare the activities of the B cells in the light and dark zones.
3. Activation-induced cytodine deaminase (AID or AICD) is involved in what GC process(es)? Deamination of a deoxycytodine results in the creation of what dNTP?
4. Draw an AID mutational hotspot that has the sequence DGYW and the antisense sequence WRCH. Where would AID make a mutation? What region of the Fab contains high numbers of these sequences?
5. What are the possible outcomes when DNA repair machinery “fixes” the base pair mismatch caused by AID? What happens if DNA repair machinery doesn’t get involved?
   1. Uridine glycosylation + short-patch base excision repair
   2. Mismatch repair
   3. No repair
6. What effect does having many WGCW sequences (antisense = DGCD) in the “switch” regions of the heavy chain locus when AID is active?

Bonus: How is this related to genomic editing with CRISPR?

7. A B cell cannot switch from expressing IgE antibodies to IgG1 antibodies. Why?
8. Why, in figure 12-16, is the response to 2^o Ag so different than 1^o antigen?