The conversion of an enhancing factor to a suppressor factor by the formation of an aggregate molecule.

A non-specific suppressor factor, owl monkey suppressor factor, OMSF, from leukaemic owl monkey peripheral T lymphocytes has been isolated and characterized. OMSF is a glycoprotein of a molecular weight of 66,000 which can be produced from purified owl monkey enhancing factor, OMEF, by both Tris buffer dialysis and by repeated freezing and thawing. SDS gel electrophoresis demonstrates that OMSF is composed of 39,000 mol. wt subunits which co-migrate with the OMEF molecule. This suppressor acts at less than nanogram levels on day 0 of the in vitro immune response to suppress the number of plaque-forming cells produced to sheep red blood cells in a murine assay system and has little effect when added on day 2 to this system. OMSF is bound by antibodies raised specifically against OMEF and inhibits the binding of OMEF to this antiserum in a competitive radioimmunoassay. These results suggest that both enhancement and suppression of the immune response can be mediated by the same molecule under different circumstances.