A peritoneal fluid activator for histamine release from isolated peritoneal mast cells of the rat.

A factor present in rat peritoneal fluid has been found to be necessary for optimal release of histamine from peritoneal mast cells by dextran and antigen, but not by concanavalin A. Washed peritoneal mast cells suspended in a physiological medium containing bovine serum albumin require ten-fold higher concentrations of phosphatidyl serine for optimal release by concanavalin A. The peritoneal fluid activator is probably a protein of molecular weight about 180,000 Daltons.