Fig. 4. Rac2^D57N expression in bone-marrow-derived macrophages inhibits M-CSF-stimulated macropinocytosis. (A) M-CSF stimulates macropinocytosis in untransfected macrophages. Cells plated on coverslips were deprived of M-CSF in the presence of 10% serum. Cells were subsequently unstimulated (basal) or stimulated for 5 minutes with 100 ng ml^-1 recombinant M-CSF. Subsequently, both basal and stimulated cells were incubated for 5 minutes with lucifer yellow (LY). LY uptake was observed by immunostaining with an antibody to LY. (B) Macrophages were transfected as described in Materials and Methods, and treated as described above. (Top) MCSF-stimulated macrophages that were immunostained for LY to show macropinocytosis. (Bottom) EGFP-positive cells indicating transfected cells. Scale bar, 10 µm. (C) Quantification of macropinocytosis. Data shown are the percentage of transfected cells with five or more macropinosomes under basal or M-CSF-stimulated conditions. Data are expressed as the mean ± s.e.m. of a minimum of 60 cells examined from three independent experiments. ^*, M-CSF-stimulated macropinocytosis by Rac2^D57N-expressing macrophages was statistically different from M-CSF-stimulated vector-expressing or wild-type cells (P<0.005).