The immunoregulatory effect of macrophage-specific PPAR gamma deficiency on experimental inflammatory bowel disease

Inflammatory bowel disease (IBD) is a condition characterized by severe intestinal inflammation and immune cell activation. The severity of the disease can be mitigated by compounds which activate peroxisome proliferator-activated receptor gamma (PPAR gamma), a receptor present widely in tissues involved in IBD pathogenesis. Our objective was to assess the affect of macrophage-specific deficiency of PPAR gamma on peripheral and colonic immune populations and colonic gene expression in experimental IBD. Macrophage-specific PPAR gamma-deficient mice (PPAR gamma flfl Lysozyme M Cre+) and control (PPAR gamma flfl Lysozyme M Cre-) littermates were treated with 2.5% dextran sodium sulfate (DSS) for 7 days. Disease activity was recorded daily and immune cell populations in the blood, spleen, mesenteric lymph nodes (MLN), and lamina propria were examined by flow cytometry. Colonic gene expression was assessed by real time PCR and microarray analyses. Our findings show that macrophage PPAR r-deficiency significantly exacerbates DSS inflammation. CD4+CD25+FoxP3+ regulatory T cells (T-regs) were significantly reduced in Cre+ mice, and MLN macrophages and CD40 expression were enhanced. There were significant differences in the number colonic macrophages between Cre+ and Cre- mice, but those from Cre+ mice expressed more CD40, Ly6C, and TLR-4. PPAR r-deficiency also increased the percent of CD8+ T cells in the lamina propria and enhanced colonic interferon gamma expression. Our findings indicate that macrophage PPAR gamma deficiency augments the severity of DSS colitis by reducing peripheral T-regs and increasing colonic macrophage activation and T cell inflammation.

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