α-Galactosylceramide suppresses murine eosinophil production through interferon-γ-dependent induction of NO synthase and CD95

Background and Purpose-Galactosylceramide (-GalCer), a pleiotropic immunomodulator with therapeutic potential in neoplastic, autoimmune and allergic diseases, activates invariant natural killer T-cells throughCD1-restricted receptors for -GalCer on antigen-presenting cells, inducing cytokine secretion. However the haemopoietic effects of -GalCer remain little explored. Experimental Approach-GalCer-induced modulation of eosinophil production in IL-5-stimulated bone marrow cultures was examined in wild-type (BALB/c, C57BL/6) mice and their mutants lacking CD1, inducible NOS (iNOS), CD95 and IFN-, along with the effects of lymphocytes; IFN-; caspase and iNOS inhibitors; non-steroidal anti-inflammatory drugs (NSAIDs) and LTD4; and dexamethasone. Key Results-GalCer (10(-6)-10(-8)M) suppressed IL-5-stimulated eosinopoiesis by inducing apoptosis. -GalCer pretreatment in vivo (100gkg(-1), i.v.) suppressed colony formation by GM-CSF-stimulated bone marrow progenitors in semi-solid cultures. -GalCer and dexamethasone synergistically promoted eosinophil maturation. Suppression of eosinophil production by -GalCer was prevented by aminoguanidine and was undetectable in bone marrow lacking iNOS, CD95, CD28; or CD1d. Separation on Percoll gradients and depletion of CD3+ cells made bone marrow precursors unresponsive to -GalCer. Responsiveness was restored with splenic lymphocytes. Experiments with (i) IFN--deficient bone marrow, alone or co-cultured with spleen T-cells from wild-type, but not from CD1d-deficient, donors; (ii) IFN- neutralization; and (iii) recombinant IFN-, showed that these effects of -GalCer were mediated by IFN-. Effects of -GalCer on eosinophil production were blocked by LTD4 and NSAIDs. Conclusions and Implications-GalCer activation of IFN--secreting, CD1d-restricted lymphocytes induced iNOS-CD95-dependent apoptosis in developing eosinophils. This pathway is initiated by endogenous regulatory lymphocytes, antagonised by LTD4, NSAIDs and aminoguanidine, and modified by dexamethasone.