Impaired distribution of CFU-GM and CFU-M. (A) Decreased spleen-derived CFU-GM and CFU-M colonies in CD44^−/− mice. The specific kinds of CFU-C in the spleens of G-CSF treated and untreated CD44^−/− and ^+/− mice were characterized and counted separately for each mouse to determine the numbers of CFU-E/BFU-E, CFU-E/Meg, CFU-G, CFU-M, and CFU-GM. The bar graph shows reduced increases of CFU-GM and CFU-M in CD44^−/− (open) compared with CF44^+/− (crosshatched) mice. Increases represent (specific colony) ratios for G-CSF-treated and -untreated animals. (B) Altered tissue distribution of CSF-GM colonies in CD44^−/− mice after G-CSF treatment. GM-CSF colony number derived from bone marrow (BM), spleen, and peripheral blood of CD44^−/− and CD44^+/− mice were compared at the indicated time points after the start of G-CSF treatment. The quotient of CFU-GM colonies from CD44^−/− and CD44^+/− were given for BM (closed squares), spleen (closed triangles), and PB (closed circles). Similar data were obtained from four independent tests with pools of two to five mice per group/experiment. The data show that at all times examined, CD44^−/− mice have fewer progenitors in the spleen than +/− control littermates (ie, ratio < 1). Conversely, CD44^−/− mutants have elevated numbers of CFU-GM progenitors in the bone marrow compared with +/− control mice (ie, ratio < 1).