Platelet‐activating factor and macrophages. I. Evidence for the release from rat and mouse peritoneal macrophages and not from mastocytes

Platelet-activating factor (PAF) is a phospholipid mediator of anaphylaxis, released from basophils of several mammalian species, that aggregates platelets and releases their vasoactive amines. The ionophore A23 187 induced the release of PAF from rat and mouse peritoneal cells, a mixed cell population that was fractionated using 5--15% Ficoll gradients and adherence to plastic petri dishes. PAF was associated with large, acid phosphatase-containing, adherent mononuclear cells. Mastocytes did not release PAF but released histamine by the action of ionophore or 48/80; they could not be held responsible for inactivation of PAF or inhibition of the PAF-induced platelet aggregation. These data indicate that, besides blood basophils, peritoneal macrophages are a likely source for PAF, a result that adds a new important function to the macrophage:aggregation of platelets and liberation of their inflammatory and vasoactive substances.