A high expression of TLR4 supports the involvement of lipopolysaccharides (LPS) in nonalcoholic fatty liver disease (NAFLD)

Abstract

Background and Aims: Toll-like receptor (TLR) 4, involved in lipopolysaccharides (LPS) recognition, is expressed by subsets of memory activated T cells. Increased LPS levels in non alcoholic fatty liver diseases (NAFLD) might be involved in its immunpathogenesis. We aimed to evaluate TLR4 expression in circulating and intrahepatic central/effector memory lymphocytes. Also to characterize intrahepatic T cell differentiation in NAFLD. Methods: Peripheral blood mononuclear cells (PBMC) and liver biopsies were obtained [25 adult patients (NAFLD); 20 healthy controls (Co)]. Total or CD45RO+ PBMC and liver cell suspensions were stained (anti-CD4/-CD8)/-CCR7/-TLR4 mAbs) and analyzed by flow cytometry. A CCR7 index (ICCR7 CD4+ or CD8+ = % CCR7+/CCR7−) was calculated. IFN-g, CCL20 and T-bet intrahepatic expression was evaluated by real-time PCR, 2−DDCt method and Mann–Whitney test. Results: ICCR7 CD4+ and CD8+ are decreased in total PBMC (p = 0.007 and 0.004) and CD45RO+ PBMC (p < 0.001 and <0.001, NAFLD vs. Co). Similar % TLR4+ CCR7+ (p = ns) but increased % TLR4+ CCR7− within CD4+ and CD8+ PBMC (p = 0.020 and 0.020, NAFLD vs. Co) were found. %CD4+ and TLR+CD4+ intrahepatic cells are increased in NAFLD (p = 0.030 and 0.020, vs. Co) whereas both CD4+ and CD8+ infiltrating cells showed lower ICCR7 (p = 0.007 and 0.004, vs. Co). IFN-g, T-bet and CCL20 mRNA intrahepatic expression was increased in NAFLD (p = 0.008, <0.001 and 0.012, vs. Co). Conclusions: CCR7− effectors cells and Th1 differentiation are predominant in NAFLD liver. An overall higher expression of TLR4 supports the involvement of lipopolysaccharides in the maintenance of a Th1/citotoxic biased response in NAFLD.