Reduced colony-stimulating capacity of SCM from G−/−GM−/− mice. Pokeweed mitogen–stimulated SCM was prepared from 4 G−/−GM−/− mice and age- and sex-matched wild-type mice using standard methods,11 and assayed for colony-stimulating capacity using G+/+GM+/+ C57BL/6 bone marrow in triplicate semisolid agar cultures with serial 1:2 dilutions of SCM as stimuli. Colonies were scored at 7 days. Results are shown as the mean ± 1 SD for 4 experiments per genotype. At the highest SCM concentration, the mean absolute numbers of pure granulocyte (1.4 v 12.9), pure macrophage (3.2 v 24.4), and mixed granulocyte/macrophage (10.0 v 42.6) colonies formed were all lower with G−/−GM−/− media v wild-type.