Immunomodulating activities associated with the cytosol fraction of a 3-methylcholanthrene-induced rat fibrosarcoma.

Cytosol fraction(s) from McFiFi2(s) fibrosarcoma cells (Fcc), isolated from either cultured cells or solid tumors induced in F344 rats, produced a dose-related inhibition of lymphoproliferative responses to several mitogens, whatever the lymphoid organ or the animal species used as the source of lymphocytes. Only stimulated human lymphocytes were not Fcc inhibited; instead, Fcc was a potent stimulator of their spontaneous proliferation. Fcc cytostatic activity was not effective in various cycling cell lines and was restricted to mitogen-stimulated lymphocytes. Fcc, a primary tumor product, did not induce suppressive cells and was unable to prevent mitogen cell surface binding. However, expression of its modulating effect was accelerated by the simultaneous presence of the mitogen. Moreover, Fcc produced its suppression by interrupting lymphocyte activation at some point within the G0-G1-phase transition. Molecular sieving showed that Fcc contains at least two factors with suppressive (mol wt, approximately 3,000) and stimulatory (mol wt, greater than 5,000) activities, respectively.