MCs promote proliferation of naive B cells and activated B cells. Naive (B) or activated (Bact) mouse B cells were labeled with CFSE and cocultured with nonsensitized mast cells (MCs) or IgE-sensitized MCs stimulated with the antigen DNP (MC/IgE-Ag). The statistical analyses of CFSE data from 3 independent experiments with naive B cells (A) or activated B cells (C) are expressed as percentages of cells in each generation and presented as means ± SD. P indicates the parent generation. Proliferation index of naive B cells (B) and activated B cells (D) is 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. Results shown are the mean of at least 3 separate experiments from 3 different MC cultures. *P < .05.