Demonstration that platelet-activating factor is capable of activating mast cells and inducing a chemotactic response.

Platelet-activating factor (PAF) is generated in a variety of inflammatory conditions in which mast cells accumulate. However, little is known about the ability of PAF to influence mast cell function directly. In this study we examine the ability of PAF to activate mast cells and regulate mast cell chemotaxis. PAF was found to induce intracellular calcium mobilization and chemotactic responses in both murine and human mast cells. PAF induced transient increases in intracellular Ca2+ concentrations with a 50% effective dose of 1 nM and induced significant migratory responses at PAF concentrations of 1 nM to 1 microM in the human leukaemia mast cell line (HMC-1). Using signal transduction inhibitors, both PAF-induced calcium mobilization and migration of mast cells were shown to require activation of pertussis toxin-sensitive G proteins. PAF-induced calcium and chemotactic responses were cross-desensitized by C5a. Together, these data demonstrate that PAF is capable of activating distinct signalling pathways in mast cells associated with calcium mobilization and cell migration; and that PAF may thus contribute to the regulation of mast cell responses and hyperplasia at sites of inflammation.