The enhancement of B-cell proliferation by MCs requires cell-cell contact and soluble factors. Naive or activated B cells were labeled with CFSE and cocultured for 72 hours with activated MCs separated or not by a transwell membrane. The statistical analyses of CFSE data of B cells in contact (A) or separated (C) by a transwell (TW) are expressed as percentages of cells in each generation and presented as means ± SD of 3 separate experiments from 2 different MC cultures. Open and black histograms represent the percentage of naive (B) and activated (Bact) B cells in each generation, respectively; P indicates the parent generation. Results of proliferation index are expressed as fold induction over B cells alone, where the proliferation index average ± SD of naive B and activated B cells alone was fixed to 1 in panels B and D, respectively. *P < .05.