We have previously suggested that two lymphokine activities-macrophage activating factor (MAF) and gamma interferon (IFN-gamma)-are mediated by the same molecule. Striking similarities were noted in their cellular biosynthesis, rate of inactivation with acid treatment and heating, and elution profiles on Sephacryl S-200. In addition, highly specific polyclonal antibodies to murine IFN-gamma neutralized MAF and IFN-gamma to a similar degree. However, definitive studies require a pure product and we now report that murine IFN-gamma that had been cloned and expressed in a simian nonlymphoid cell line shows MAF activity. But it is not yet known whether IFN-gamma is responsible for all the MAF activity in media conditioned by T cells as the possibility for MAF heterogeneity remains.

The antibacterial properties of statolon and pyran were compared with those of bacterial endotoxin and found to be similar. Although high resistance was transient, it was followed by immunity of the same order as in mice infected without pre-treatment with the interferon inducers.

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Murine spleen lymphoid cells treated with insoluble (Sepharose bound) concanavalin A elaborate Gamma (immune) interferon (IFN-gamma) and macrophage activation factor (MAF) into the culture medium. Similarly, MAF is produced by T cells with other IFN-gamma inducers. MAF induces resting (noncytotoxic) macrophages to become tumoricidal. We have compared various physicochemical properties of MAF and INF-gamma, their neutralization by antibody to IFN-gamma, and their induction period. In these parameters, induction of antiviral activity was compared to induction of macrophage tumoricidal activity. All of the parameters studied have given results that demonstrate close similarity in the physical properties, molecular characteristics, and biological reactivities of the two lymphokines, and this similarity suggests that these two lymphokines reside in the same molecule. This conclusion would include that IFN-gamma, like IFN-alpha and IFN-beta, is capable of activating macrophages to become cytotoxic toward tumor cells.

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