In vivo MMC sensitivity of CFC from BM and spleen cells of Fac +/+ and Fac −/− mice. (A) The number of CFC established 2 and 6 days after a single MMC injection (0.75 mg/kg). (B and C) The number of CFC in BM (B) and spleen (C) after 1, 3, and 5 weekly injections of MMC (0.3 mg/kg). Controls represent saline-injected mice. Data represent the mean ± SEM of triplicate determinations from 2 mice. Significant differences between controls and MMC-injected mice (*P < .01; **P < .05; #P < .005; ##P < .0005). The absence of SEM bars represents values too low to appear in the graph.