Brief Definit ive Report The Rockefeller University Press $30.00

Rearranged Ig V(D)J genes in B cells responding to infections or vaccinations mutate somatically at an 1 million-fold higher rate than back-ground mutations (Di Noia and Neuberger, 2007). Rare mutations that improve affinity are selected by competition between B cells to capture antigen via surface expression of their mutated Ig and to present antigen-derived peptides to follicular helper T cells. This res-cues the presenting cells from programmed cell death (Allen et al., 2007). Ig class switching, a change from production of IgM to production of IgG, IgA, or IgE, frequently precedes or is concurrent with V(D)J point mutation. Class switching occurs via nonhomologous joinin