PAF-releasing factor in human serum and inflammatory exudate.

A factor responsible for releasing PAF produced in stimulated human polymorphonuclear leukocytes, which had been previously reported in human serum (Miwa et al. (1992) J. Immunol. 148, 872-880), was also confirmed to be present in inflammatory exudate. PAF-releasing factor, partially purified from human serum, was shown to possess higher affinity for PAF than for triacylglycerol, cholesterol ester, fatty acid or phosphatidylcholine. PAF bound to this factor aggregated washed rabbit platelets to the same extent as that bound to BSA, but was difficult to be hydrolyzed using PAF acetylhydrolase. These observations strongly suggest that PAF-releasing factor functions as a PAF carrier in blood and in the inflammatory response.