IFN-γ stimulates cell proliferation of IRF-1 antisense retrovirus-transfected KG1a cells. (A) Cells were stimulated with increasing concentration of IFN-γ, and the viable cell number was counted on day 4 of cultures. (B) Time course study of the effects of IFN-γ on the growth of pG1IRF-1AS–transfected and pG1NA-transfected (control) KG1a cells. Statistical analysis (t-test): **P < .01 when compared with the value without IFN-γ. Similar results were obtained in two independent experiments.