Inhibition of human granulocyte-macrophage colony formation by interleukin 2-treated lymphocytes is mediated by interferon gamma and tumor necrosis factor alpha

We previously demonstrated that human granulocyte-macrophage colony (granulocyte-macrophage colony-forming units, CFU-GM) formation was inhibited by interleukin 2 (IL-2)-treated lymphocytes and their conditioned medium (CM). In the present study, the mechanism of this suppression was investigated. When anti-interferon (IFN)-gamma antibody or anti-tumor necrosis factor (TNF)-alpha antibody was added to CFU-GM agar culture with IL-2-treated lymphocytes or their CM, the inhibition of CFU-GM colony formation was partially abrogated, whereas anti-TNF-beta antibody did not abolish the inhibitory effects. When anti-IFN-gamma and anti-TNF-alpha antibodies were added simultaneously, full recovery of colony formation was observed. In the CM of IL-2-treated lymphocytes, detectable levels of IFN-gamma (81 +/- 15 U/ml) and TNF (3.1 +/- 1.1 U/ml) were found. Addition of IFN-gamma and TNF-alpha at these concentrations to the agar culture inhibited CFU-GM colony formation. Taken together, these results indicate that inhibition of human CFU-GM colony formation by IL-2-treated lymphocytes and their CM is mediated by IFN-gamma and TNF-alpha generated from IL-2-treated lymphocytes.