Interferon gamma: more than a MAF.

The precise immunoregulatory activities of particular lymphokines have been difficult to define due to the presence of contaminating molecules in the purified natural preparations under study. Thus, the application of recombinant DNA technologies to lymphokine research has been instrumental in elucidating the biologic properties of many of these factors. In particular, with the availability of recombinant gamma interferon (rIFN-gamma) a variety of immuno-regulatory functions, including natural killer activation, enhancement of lymphokine production, macrophage activation, and cell surface Ia expression, have been clearly shown to be mediated by this lymphokine. Recently we have compared the properties of macrophage activating factor (MAF) to those of natural and rIFN-gamma. This article reviews our evidence suggesting that IFN-gamma is a major MAF. In addition, we present evidence for another activity of IFN-gamma, namely, its ability to regulate the growth of certain interleukin 2 (IL-2)-dependent cytotoxic T cell lines.