Interferon gamma produced by mitogen-activated T lymphocytes does not directly mediate lymphoproliferation.

Human interferon gamma (IFN-gamma) endogenously produced during mitogenic stimulation of human peripheral blood mononuclear cells or human T lymphocyte-enriched cultures was neutralized in situ by the addition of a polyclonal antiserum (anti-L) raised in a rabbit against partially purified natural IFN-gamma derived from peripheral blood mononuclear cells. Small decreases in mitogen-induced [3H]thymidine incorporation (lymphoproliferation) were demonstrated under these conditions. However, an antiserum (anti-G) raised in a sheep against highly purified recombinant IFN-gamma (E. coli-derived) which strongly neutralized the antiviral effect of IFN-gamma either had little effect on mitogen-induced lymphoproliferation or caused slight enhancement of mitogenesis. The interleukin 2 responsiveness of activated T lymphocytes following mitogenic stimulation was not found to be different in the presence of anti-G to that of control cultures incubated in the presence of normal sheep serum. These results suggest that IFN-gamma is not a direct requirement for lymphoproliferation.