Lymphopenia and reduced CSR in RNF8^−/− mice. (A, left) Mean number of CD43⁻ cells isolated from spleens of RNF8^+/+ and RNF8^−/− mice. (middle) Mean number of thymocytes in RNF8^+/+ and RNF8^−/− mice (error bars = SD; n ≥ 3). (right) TCRβ surface expression in freshly isolated RNF8^+/+, RNF8^−/−, and 53BP1^−/− thymocytes (one representative out of three independent experiments). (B) Two-color flow cytometric analysis of IgG1 expression on CFSE-labeled B cells that were stimulated with LPS plus IL-4 for 4 d (percentages are shown). (C) Frequency of IgG1 and IgG3 expression in B cells that were stimulated for 4 d with LPS plus IL-4 or LPS alone in five or three independent experiments, respectively. Horizontal bars indicate means. (D) Representative example of CFSE incorporation profiles of B cells stimulated with LPS plus IL-4 for 4 d. (E) Percentage of cells expressing IgG1 (left) or IgG3 (right) that had undergone a given number of cell divisions. One representative out of at least three independent experiments is shown in D and E.