The Rockefeller University Press $30.00
J. Exp. Med. Vol. 206 No. 2 477-490
In T celldependent antibody responses, B cells
are triggered to undergo a second round of anti-
body diversification in germinal centers (GCs) (1).
tations into rearranged variable (V) regions of
Ig genes allowing antibody affinity matura-
tion (2, 3), whereas class switch recombination
(CSR) exchanges the Ig constant (C) region to
modify the effector function of the antibody (4).
Both SHM and CSR rely on activation-in-
duced deaminase (AID), an enzyme which de-
aminates cytidine residues in single-stranded
DNA (5). The DNA deamination model of
SHM suggests the conversion of G-C basepairs