Splenic B cells from Mlh1^GR/GR mice show decreased switching efficiencies in ex vivo cultures. (A) Representative FACS results from WT and Mlh1^GR/GR cells stimulated with LPS or LPS + IL4 for 4 d. Percentages of switched cells are indicated within the gates. (B) The mean efficiency of switching in the WT group within each experiment was defined as 100%. Mean percentages of switching ± SEM are shown. Significance was determined using the two-tailed unpaired Student’s t test (***, P < 0.001). Data correspond to six WT and seven Mlh1^GR/GR mice assayed in two different experiments. (C) Overlay histograms of intracellular CFSE signal from splenic B cells stimulated with LPS + IL4 for different periods of time.