Isolation of a lipid-soluble histamine release factor from human platelets

We have isolated a histamine release factor from human platelet supernatants by heparin column chromatography, gel filtration and reversed phase HPLC. Fractions from each chromatographic step were assayed for histamine release factor activity (HRF). A peak of HRF activity was detected at a molecular mass of 60 kDa. Subsequent HPLC purification showed that the factor co-eluted with human serum albumin, but was totally extractable into the lipid phase. Comparison of biological activity with known basophil and eosinophil-activating hydroxyeicosanoids demonstrated similar activity with 5(S)-hydroperoxy-6E,8Z,11Z,14Z-eicosatetraenoic acid (5(S)-HPETE). The identification of this lipid soluble HRF demonstrates the novel potential role of an as yet unidentified lipid as an HRF, in the absence of priming stimuli.