Fig. 1.

Post-meiotic segregation 2 (PMS2) acts on double-strand DNA breaks during class-switch recombination. B cells were stimulated by soluble CD40 ligand and interleukin-4 for 5 days for class-switch recombination. Double-strand breaks (DSB) in the DNA of switch regions (Sµ) were detected by a ligated-mediated polymerase chain reaction (PCR). PCR products were transferred to agarose gels and hybridized with a labelled Sµ probe. Very few double-strand breaks were observed in the B cells from the two PMS2-deficient patients (P1, P3) compared with healthy controls (Ctrl). AID^−/−: B cells from activation-induced cytidine deaminase patients (negative control).