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.

The class B scavenger receptor CD36 is a component of the pattern recognition receptors on monocytes that recognizes a variety of molecules. CD36 expression in monocytes depends on exposure to soluble mediators. We demonstrate here that CD36 expression is induced in human monocytes following exposure to IL-13, a Th2 cytokine, via the peroxisome proliferator-activated receptor (PPAR)c pathway. Induction of CD36 protein was paralleled by an increase in CD36 mRNA. The PPARc pathway was demonstrated using transfection of a PPARc expression plasmid into the murine macrophage cell line RAW264.7, expressing very low levels of PPARc, and in peritoneal macrophages from PPARc-conditional null mice. We also show that CD36 induction by IL-13 via PPARc is dependent on phospholipase A2 activation and that IL-13 induces the production of endogenous 15-deoxy-D 12,14 -prostaglandin J 2 , an endogenous PPARc ligand, and its nuclear localization in human monocytes. Finally, we demonstrate that CD36 and PPARc are involved in IL-13-mediated phagocytosis of Plasmodium falciparum-parasitized erythrocytes. These results reveal a novel role for PPARc in the alternative activation of monocytes by IL-13, suggesting that endogenous PPARc ligands, produced by phospholipase A2 activation, could contribute to the biochemical and cellular functions of CD36.Leukocyte signaling * These 2 authors contributed equally to this work. IntroductionThe innate immune system protects the host in the early phase of infection. Circulating monocytes and tissue macrophages (Mu) mediate much of this innate immune response [1]. The strategy of recognition in the innate response is mediated by the coordinated action of pathogen-associated molecular patterns and pattern recognition receptors. Scavenger receptors and mannose receptor are important pattern recognition receptors in monocytes/Mu [2,3]. The modulation of the expression of these receptors may be critical in the role of these cells in antigen processing, scavenging, and host defence against pathogens. Several members of the scavenger receptor family, including Mu class A scavenger receptors and CD36, have been identified as receptors for modified lipoproteins on Mu, and their relevance to lipid uptake has been demonstrated in vitro and in vivo [4]. The scavenger receptor CD36, an 88-kDa integral membrane protein, is a class B scavenger receptor expressed on a wide variety of cells, in particular on monocytes and monocytederived Mu [5,6]. CD36 is known as a receptor for the uptake of oxidatively modified low-density lipoprotein (LDL) [7] and is also able to bind anionic phospholipid phosphatidylserine [8]. This scavenger receptor is implicated in the clearance of apoptotic cells [9]. Recently, McGilvray and colleagues [10] described a CD36-dependent nonopsonic phagocytosis of erythrocytes containing P. falciparum, by monocytes and culture-derived Mu, and a decrease in the parasiteinduced TNF secretion by monocytes/Mu. These processes were accentuated by CD36 up-regulation by peroxisome proliferator-acti...