Mast cells are central regulators of allergic inflammation through production of various chemical mediators and cytokines. Bacterial infection occasionally worsens allergic inflammation. Although the exact mechanism of this phenomenon remains unclear, we have previously reported that LPS stimulates mast cells to produce not only pro-inflammatory cytokines, such as IL-6 and TNF-alpha, but also Th2-type cytokines, such as IL-5 and IL-13, and a regulatory cytokine, IL-10. In the present study, we have studied the effect of ceramide on LPS-mediated cytokine production from mast cells, as ceramide modulates various cellular functions in many cell types. Administration of cell-permeable C8 ceramide reduced production of IL-5, IL-10, and IL-13 from LPS-stimulated mouse bone marrow-derived mast cells (BMMCs) apparently through transcriptional inhibition, but did not affect IL-6 or TNF-alpha production. Consistently, LPS-stimulated production of IL-5, IL-10, and IL-13 from BMMCs is significantly enhanced in the presence of fumonisin B1, a de novo ceramide synthesis inhibitor. Interestingly, the same C8 ceramide treatment showed opposite effects on cytokine production from LPS-stimulated macrophages, reducing IL-6 and TNF-alpha while not affecting IL-10 production. C8 ceramide pretreatment significantly reduced LPS-induced Akt phosphorylation in BMMCs, but not in macrophages. Furthermore, pretreatment of BMMCs by wortmannin, a specific inhibitor of PI3 kinase, inhibited LPS-stimulated expression of IL-5, IL-10, and IL-13, but not that of TNF-alpha or IL-6. Thus, ceramide appeared to down-regulate LPS-stimulated production of IL-5, IL-10, and IL-13 from mast cells by inhibiting PI3 kinase-Akt pathway in a cell type-specific manner.
(c) 2007 Wiley-Liss, Inc.