Platelet activating factor: an inhibitor of neutrophil activation?

Preparations of platelet activating factor (PAF) derived by methanolic extraction of supernatants from antigen-challenged rabbit basophils proved capable of activating platelets while concurrently inhibiting neutrophil aggregation/secretion stimulated by biologically active F-Met peptides, ionophore A23187, or zymosan-treated serum. This inhibition was non-cytotoxic and species-non-specific. When these PAF preparations were analysed using thin-layer chromatography, multiple lipids were detected. Both platelet-stimulating as well as neutrophil-inhibitory activity was present in a lipid component migrating at an RF consistent with native PAF; however, these biological activities were not limited only to PAF and, indeed, could also be detected in lipid with solubility characteristics more closely related to a lysophosphatide than to native PAF. These data are compatible with the belief that native PAF may belong to a family of biologically active lipids differing somewhat in physico-chemical properties. Moreover, these data illustrate that PAF and/or PAF-like molecules may also demonstrate a biological activity distinct from their effects upon the platelet.