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Insulin-dependant Diabetes Mellitus (IDDM) is characterized' by a selective destruction of pancreatic [beta]-cells. Despite an identified genetic predisposition for the disease, the low concordance rate for diabetes development in monozygotic twins supports environmental factors such as virus infection in the development of autoimmune diabetes. EMCV has been used at low doses in genetically susceptible mice to initiate the disease, and this has been a useful tool to understand the role of macrophages in diabetes development. EMCV-induced IDDM is mediated by macrophage production of soluble mediators such as nitric oxide (NO) and IL- 1. However, the mechanisms by which EMCV stimulate macrophage activation are incompletely described. Recently, we have shown that macrophage activation is dependent upon interaction with EMCV viral coat protein, as "RNA free" empty EMCV capsids are capable of stimulating the same signaling cascades and inflammatory gene expression as intact EMCV. Herein we describe a novel role for the G-protein coupled receptor Ccr5 in mediating EMCV-stimulated signaling cascades and subsequent inflammatory gane expression in macrophages. A blocking antibody specific to the N-terminus of Ccr5 is capable of attenuating EMCV-induced MAPK activation, iNOS and IL-1 expression and NO production by macrophages. Interestingly, this antibody also attenuates dsRNA- (poly IC) and EMCV coat protein-stimulated MAPK signaling and inflammatory gene expression. These findings were confirmed using macrophages isolated from Ccr5-/- mice. EMCV-induced MAPK activation and inflammatory gene expression is attenuated in macrophages isolated from Ccr5-/--deficient mice as compared to wild type control macrophages. These findings provide biochemical evidence that macrophage activation in response to EMCV is mediated in part by Ccr5, and that this inflammatory activation is the result of an interaction with EMCV coat protein. In addition, these findings suggest that Ccr5 may also function as the elusive cell surface receptor for poly IC. [ABSTRACT FROM AUTHOR]

Double-stranded (ds) RNA, both synthetic and produced during virus replication, rapidly stimulates MAPK and NF-κB signaling that results in expression of the inflammatory genes inducible nitric oxide synthase, cyclooxygenase 2, and IL-1β by macrophages. Using biochemical and genetic approaches, we have identified the chemokine ligand-binding C-C chemokine receptor type 5 (CCR5) as a cell surface signaling receptor required for macrophage expression of inflammatory genes in response to dsRNA. Activation of macrophages by synthetic dsRNA does not require known dsRNA receptors, as poly(inosinic:cytidylic) acid [poly(I:C)] activates signaling pathways leading to expression of inflammatory genes to similar levels in wild-type and Toll-like receptor 3- or melanoma differentiation antigen 5-deficient macrophages. In contrast, macrophage activation in response to poly(I:C) is attenuated in macrophages isolated from mice lacking CCR5. These findings support a role for CCR5 as a cell surface signaling receptor that participates in activation of inflammatory genes in macrophages in response to the viral dsRNA mimetic poly(inosinic:cytidylic) acid by pathways that are distinct from classical dsRNA receptor-mediated responses.

Among several bacterial and viral pathogens, the atypical fungal organism Pneumocystis jirovecii has been implicated as a contributor to the pathogenesis of chronic obstructive pulmonary disease (COPD). In a previous study, we reported that Pneumocystis-colonized HIV-positive subjects had worse obstruction of airways and higher sputum levels of macrophage elastase/matrix metalloproteinase 12 (MMP12), a protease strongly associated with the development of COPD. Here, we examined parameters of Pneumocystis-induced MMP12 in the lungs of mice and its role in the lung immune response to murine Pneumocystis. Initial studies demonstrated that P. murina exposure induced Mmp12 mRNA expression in whole lungs and alveolar macrophages (AMs), which was dependent on the presence of CD4+ T cells as well as signal transducer and activator of transcription 6. Mmp12 mRNA expression was upregulated in AMs by interleukin (IL)-4 treatment, but downregulated by interferon (IFN)-γ, indicating preferential expression in alternatively activated (M2a) macrophages. IL-4 treatment induced the 54-kDa proenzyme form of MMP12 and the 22-kDa fully processed and active form, whereas IFN-γ failed to induce either. Despite a reported antimicrobial role in macrophage phagolysosomes, mice deficient in MMP12 were not found to be more susceptible to lung infection with P. murina. Collectively, our data indicate that MMP12 induction is a component of the P. murina-induced M2 response and thus provides insight into the link between Pneumocystis colonization/infection and exacerbations in COPD.