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Hepoxilins have previously been shown to release intracellular calcium in human neutrophils. We show herein that tritium-labeled hepoxilin A3 of high specific radioactivity binds to human neutrophils, and this binding is reversed by the addition of unlabeled compound, demonstrating that specific binding for these compounds exists in these cells. Specific binding of both the methyl ester derivative as well as the free acid form of the hepoxilin takes place in broken membrane fragments. In contrast only the methyl ester derivative binds specifically to the intact cells. We also show that intact neutrophils form hepoxilin A3 when incubated in the presence of the hepoxilin precursor, 12(S)-HPETE. These data demonstrate that hepoxilin synthesis can occur in the neutrophil and that hepoxilin binding sites, which appear to be located intracellularly, exist in these cells.

We have shown previously that interleukin 8 (IL-8) induces histamine and leukotriene release in human basophils exposed to interleukin 3 (IL-3). We now found that pretreatment with low concentrations of IL-8 selectively inhibits this response. Inhibition was significant at 0.01 nM IL-8 and virtually complete at 1 nM, which is about 100-fold lower than the concentration required for induction of mediator release. IL-8 dependent responses were also inhibited, albeit to a lesser extent, by preincubation with neutrophil-activating peptide 2 (NAP-2), but not with connective tissue-activating peptide III (CTAP-III) or platelet factor 4 (PF4). Release induced by C5a, fMet-Leu-Phe, or anti-IgE antibody, by contrast, was not affected.

The relative rates of cysteinyl-leukotriene metabolism were analyzed in fresh human and mouse serum. Human serum contained higher gamma-glutamyl-transpeptidase activity than mouse serum, and a higher percentage of the metabolized leukotriene C4 was recovered as leukotriene D4 in the human serum than in the mouse serum. The results suggest that the patterns of metabolism of the cysteinyl-leukotrienes could be an important factor in determining the relative sensitivity of an animal to the development of hypersensitivity reactions.