Rosette-increasing factor released by PHA-stimulated mononuclear cells in vitro which augments active E and EA rosette formation.

The supernatants of phytohaemagglutinin (PHA) stimulated mononuclear (MN) cells contained a factor that significantly increased active E and EA (IgG) RFC which belonged to T cells and such was termed 'rosette-increasing factor' (RIF). This factor was demonstrated after as early as 2 hr of cluture and remained stable thereafter. The production of the factor seemed to be independent of macrophages and was mainly by nylon wool-adherent T cells. Cycloheximide and cytochalasin B pretreatment of MN cells prior to the addition of PHA abolished the activity of the supernatants in a dose-dependent manner, whereas mitomycin C and colchicine had no effect. As active E-RFC and Fc (IgG) receptor-positive T cells are considered to be closely correlated with cell-mediated immunity, this factor may play an important role in cellular immune response.