Macrophage mannose receptor (MMR) is an important component of the innate immune system implicated in host defense against microbial infections such as candidiasis and in antigen presentation. We demonstrate here that the MMR expression is induced in mouse peritoneal macrophages following exposure to PPARgamma ligands or to interleukine-13 (IL-13) via a PPARgamma signaling pathway. Ligand activation of the PPARgamma in macrophages promotes uptake, killing of Candida albicans, and reactive oxygen intermediates production triggered by the yeasts through MMR overexpression. We also show that MMR induction by IL-13 via PPARgamma is dependent on phopholipase A2 activation and that IL-13 induces 15d-PGJ2 production and nuclear localization. These results reveal a novel signaling pathway controlling the MMR surface expression and suggest that endogenous PPARgamma ligand produced by phospholipase A2 activation may be an important regulator of MMR expression by IL-13.

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We studied the effects of interferon-gamma (IFN-gamma), a Th1 cytokine, and interleukin-13 (IL-13) or interleukin-4 (IL-4), Th2 cytokines, on the antifungal activity of resident murine peritoneal macrophages against Candida albicans 'in vitro'. IFN-gamma, IL-13 and IL-4 treatment enhanced the candidastatic functions of the macrophages. Reactive oxygen intermediates (ROIs) seem to be directly involved in the increase of anti-Candida activity in macrophages treated with Th1 or Th2 cytokines. Study of unopsonized C. albicans phagocytosis showed that IFN-gamma reduces the uptake process whereas the Th2 cytokines increase it. This difference is correlated to mannose receptor expression, which is decreased by IFN-gamma but increased by the Th2 cytokines. So, the effects on phagocytosis and candidastatic activity of IFN-gamma-treated macrophages are dissociated. In contrast, the phagocytic ability of macrophages pretreated 'in vitro' with IL-4 or IL-13 played a complementary role to the ROIs, in reduction of yeast proliferation by macrophages. In consequence, the macrophages treated with IL-13 and IL-4 develop a higher fungistatic activity than macrophages activated by IFN-gamma. Amphotericin B associated with IL-13 or IFN-gamma, but not with IL-4, enhanced the yeast growth inhibition activity of macrophages. The ROIs were involved in the additive effect of IFN-gamma with amphotericin B, whereas another mechanism was implicated in the increase of candidastatic activity of macrophages treated with IL-13 in association with amphotericin B.