Characterization of the macrophage subset affected and its response to a T suppressor factor (TsFmp) found in cryptococcosis.

Previous reports from our laboratory described the detection of a suppressor factor which inhibited the phagocytic activity of a macrophage subset in murine cryptococcosis and in classical models of immune tolerance. The suppressor factor was originally named PIL (phagocytosis-inhibiting lymphokine) but has recently been renamed TsFmp (T suppressor factor for macrophage phagocytosis) because it was found to resemble the antigen-specific I-J-restricted suppressor factors described by others. The current investigation revealed that TsFmp acted rapidly upon the macrophage (15 min or less) to exert its effect of inhibiting the phagocytic process. The time for the macrophage to recover from the effects of TsFmp was likewise very rapid. The ability of TsFmp to inhibit phagocytosis was limited to engulfment of particles by Fc and mannan receptors and did not extent to phagocytosis via complement receptors or by nonspecific mechanisms. The macrophage subset that responded to TsFmp was determined to be in the I-A+ and I-J-IM+ subset.