Stimulation of equine eosinophil migration by hydroxyacid metabolites of arachidonic acid

Lipoxygenase products of arachidonic acid are important mediators of inflammation, affecting several aspects of cell function. Monohydroxyeicosatetraenoic acid (mono-HETE) and 5,12-dihydroxyeicosatetraenoic acid (LTB4) enhance migration of both neutrophils and eosinophils in several species. The relative ability of positional isomers of HETE and of LTB4 to affect migration of equine eosinophils was studied. The 5, 8, 9, 11, 12, and 15 isomers of HETE were prepared by autooxidation of arachidonic acid, separated by sequential normal phase and reverse phase high performance liquid chromatography, and their identities verified by gas chromatography-mass spectrometry. Equine eosinophils were isolated to 30-70% purity on discontinuous metrizamide gradients. All isomers of HETE stimulated directed migration (chemotaxis) at concentrations ranging from 10(-5) to 10(-8) M. The relative activities of isomers were 11 greater than 9 = 8 = 5 greater than 12 greater than 15. The dihydroxy acid LTB4 maximally stimulated chemotaxis of equine eosinophils at a concentration of 3 X 10(-7) M. The eosinophil migration that resulted was less than the maximal stimulation observed in response to isomers of HETE. The results of our study suggest that equine eosinophils are excellent indicator cells for assay of arachidonic acid metabolites with chemotactic activity. Equine eosinophils are more sensitive to chemotactic stimulation by HETEs than cells from other animal species but are far less sensitive to stimulation by LTB4.