Studies on macrophage-activating factor (MAF) in antitumor immune responses. II. Molecular characterization of MAF produced by the tumor-immune Lyt-1+2- T cell subset.

In the present study we investigated some of the physicochemical properties of macrophage-activating factor(s) (MAF) produced by the tumor-immune Lyt-1+2- T cell subset. Supernatant from mixed culture of spleen and lymph node cells, obtained from C3H/HeN mice immunized with syngeneic MH134 hepatoma or MCH-1-A1 fibrosarcoma, with the corresponding tumor cells exhibited the capability of activating peritoneal exudate macrophages to exert their cytostatic and cytolytic activities on tumor cells. Such MAF production was abolished by treatment of tumor-immune spleen and lymph node cells with anti-Thy-1.2 or anti-Lyt-1.1 antibody plus complement (C) before culturing. Anti-Lyt-2.1 and/or anti-asialo GM1 plus C treatment, however, had only marginal effect on the generation of MAF by these cells, despite the complete disappearance of natural killer (NK) cell activity of spleen and lymph node cells after the treatment with anti-asialo GM1 plus C. Thus, the tumor-specific Lyt-1+2- T cell subset could fulfill a crucial role in generating MAF without the support of NK cells. The MAF activity was heat, acid, and trypsin sensitive. On Sephacryl S-300 column, MAF activity was eluated in a broad single peak around a molecular weight (m.w.) of 70,000 daltons. Antiviral activity was detected in the concentrated pool of MAF-containing fractions from Sephacryl S-300. Gel permeation analysis using HPLC also showed a coincident peak of MAF and antiviral activities at a m.w. of approximately 70,000 daltons. In addition, MAF activity was almost completely neutralized by incubation with rabbit antiserum against recombinant murine gamma-interferon (IFN gamma). Taken together, these results indicate that MAF generated by tumor-immune Lyt-1+2- T cell subset is closely related to IFN gamma.