Identification of a novel and highly potent eosinophil chemotactic lipid in human eosinophils treated with arachidonic acid.

Purified human eosinophils generate eosinophil chemotactic lipids (ECL), when incubated with arachidonic acid without any stimulus. Reversed phase HPLC of incubation supernatants revealed major lipid-like eosinophil chemotactic activity eluting in a peak containing 5(S), 15(S)dihydroxy-6,13-trans-8,11-cis-eicosatetraenoic acid (5,15-DiHETE) as well as a 8,15-dihydroxyeicosatetraenoic acid. For further characterization of the ECL, some authentic dihydroxyeicosatetraenoic acids were tested for eosinophil chemotactic activity. Only 5,15-DiHETE as well as 8(S), 15(S)-dihydroxy-5,11-cis-9,13-trans-eicosatetraenoic acid were found to be chemotaxins for human eosinophils, however, with an ED50 near 0.3 microM and 1.5 microM, respectively. The presence of high titer eosinophil chemotactic activity in ECL preparations let us look for a contaminating ECL with higher specific activity. By using a different reversed phase HPLC-system 5,15-DiHETE as well as 8(R), 15(S)-dihydroxy-5,11-cis-9,13-trans-eicosatetraenoic acid could be separated from a highly potent ECL. Final purification of this ECL by the use of straight phase HPLC resulted in a single at 260 nm absorbing peak giving an UV spectrum different from that known for eosinophil chemotactic factors indicating a novel type of eosinophil chemotactic lipid. Eosinophil chemotactic activity of purified ECL has been found to be similar to that seen for platelet-activating factor, the most potent chemotaxin so far known, either in the number of migrating cells or the ED50. Cross-desensitization experiments with ECL, leukotriene B4, and platelet-activating factor revealed the existence of a separate ECL receptor on eosinophils. The production of potent ECL by the responder cells themselves supports the idea that there exists a self-sustaining mechanism of eosinophil accumulation.