FIG. 1.

J2-transformed macrophages require C/EBPβ for survival in the absence of exogenous GFs. (A) wt and C/EBPβ^−/− bone marrow cells were infected with J2 and maintained in GM-CSF. After 7 days, GF was removed and viable cells were measured over a time course by trypan blue exclusion. The experiment shown is representative of four independent trials. (B) GF dependence of macrophage cell lines. J2-transformed wt (J2-WT1; solid symbols) and C/EBPβ^−/− (J2-KO1; open symbols) macrophage (Mφ) cell lines were cultured in the presence (squares) or absence (circles) of 100 ng of M-CSF/ml. Cell viability was measured at 0, 24, and 48 h by neutral red dye uptake. Data are the average of four independent experiments, with standard errors indicated. (C) CFU assays. A total of 10⁴ J2-WT1 or J2-KO1 cells were plated in soft agar in the presence or absence of 200 ng of M-CSF/ml (NF, no factor). After 7 days, colonies (>50 cells) were scored. Data are the average ± standard error of the mean of two independent experiments, each performed in duplicate. Statistical analysis of the data in panels B and C was performed using the unpaired Student's t test (**, P < 0.01).