Identification of a spleen cell-derived factor that inhibits sensitization of murine peritoneal mast cells as interferon-gamma

We present evidence that a spleen cell-derived factor that inhibits the sensitization of mouse peritoneal mast cells is IFN gamma. Conditioned medium (CM) from Con A-activated mouse spleen cells and recombinant MuIFN gamma both inhibited antigen-induced 5-HT release from peritoneal mast cells when added at the sensitization stage, but were without effect on presensitized cells. Both preparations were active at dilutions corresponding to similar levels of IFN activity (1-10 units/ml). The inhibitory activity of CM was blocked by a rat monoclonal MuIFN gamma-neutralizing antibody, thus confirming that IFN gamma was the active molecule.