Fig. 3.

CSR in cells deficient in both XRCC1 and Lig4. (A) Western blot analysis of protein expression. (Lane 1) Wild type; (lane 2) XRCC1^Δ/Δ; (lane 3) Lig4^Δ/Δ; (lane 4) Lig4^Δ/Δ XRCC1^Δ/Δ. The same blot was stripped and reprobed with different antibodies as indicated. (B) Propagation of live cells (trypan exclusion) over a span of 3 d in unstimulated (−CIT) or stimulated (+CIT) cultures. Error bars indicate SD of three independent experiments. (C) Representative FACS analysis of CSR by surface staining of IgM (PE labeled) and IgA (FITC labeled) after 72 h growth in the absence or presence of cytokines (CIT). Numbers in boxed areas indicate percentages. (D) Relative CSR efficiency of various genotypes. Error bars indicated SD of at least three independent experiments (wild-type CSR efficiency set to 100%). P value was calculated by two-tailed paired t test. Comparison between XRCC1^+/Δ and XRCC1^Δ/Δ is based on five independent experiments.