Intracrine Cysteinyl Leukotriene Receptor–mediated Signaling of Eosinophil Vesicular Transport–mediated Interleukin-4 Secretion

We investigated whether cysteinyl leukotrienes (cysLT) are intracrine signal transducers that regulate human eosinophil degranulation mechanisms. Interleukin (IL)-16, eotaxin, and RANTES stimulate vesicular transport–mediated release of preformed, granule-derived IL-4 and RANTES from eosinophils and the synthesis at intracellular lipid bodies of LTC₄, the dominant 5-lipoxygenase–derived eicosanoid in eosinophils. 5-Lipoxygenase inhibitors blocked IL-16–, eotaxin-, and RANTES-induced IL-4 release; but neither exogenous LTC₄, LTD₄, nor LTE₄ elicited IL-4 release. Only after membrane permeabilization enabled cysLTs to enter eosinophils did LTC₄ and LTD₄ stimulate IL-4, but not RANTES, release. LTC₄-elicited IL-4 release was pertussis toxin inhibitable, but inhibitors of the two known G protein–coupled cysLT receptors (cysLTRs) (CysLT1 and CysLT2) did not block LTC₄-elicited IL-4 release. LTC₄ was 10-fold more potent than LTD₄ and at low concentrations (0.3–3 nM) elicited, and at higher concentrations (>3 nM) inhibited, IL-4 release from permeabilized eosinophils. Likewise with intact eosinophils, LTC₄ export inhibitors, which increased intracellular LTC₄, inhibited eotaxin-elicited IL-4 release. Thus, LTC₄ acts, via an intracellular cysLTR distinct from CysLT1 or CysLT2, as a signal transducer to selectively regulate IL-4 release. These results demonstrate that LTC₄, well recognized as a paracrine mediator, may also dynamically govern inflammatory and immune responses as an intracrine mediator of eosinophil cytokine secretion.