Toll-like receptors in pathophysiology of liver diseases

Toll-like receptors(TLRs) are pattern recognition receptors that participate in host defense by recognizing pathogen-associated molecular patterns alongside inflammatory processes by recognizing damage associated molecular patterns. Given constant exposure to pathogens from gut, strict control of TLR-associated signaling pathways is essential in the liver, which otherwise may lead to inappropriate production of pro-inflammatory cytokines and interferons and may generate a predisposition to several autoimmune and chronic inflammatory diseases. The liver is considered to be a site of tolerance induction rather than immunity induction, with specificity in hepatic cell functions and distribution of TLR. Recent data emphasize significant contribution of TLR signaling in chronic liver diseases via complex immune responses mediating hepatocyte(i.e., hepatocellular injury and regeneration) or hepatic stellate cell(i.e., fibrosis and cirrhosis) inflammatory or immune pathologies. Herein, we review the available data on TLR signaling, hepatic expression of TLRs and associated ligands, as well as the contribution of TLRs to the pathophysiology of hepatic diseases.

Dysregulation of innate immunity in ulcerative colitis patients who fail anti-tumor necrosis factor therapy

AIM To study the innate immune function in ulcerative colitis(UC) patients who fail to respond to anti-tumor necrosis factor(TNF) therapy.METHODS Effects of anti-TNF therapy, inflammation and medications on innate immune function were assessed by measuring peripheral blood mononuclear cell(PBMC) cytokine expression from 18 inflammatory bowel disease patients pre- and 3 mo post-anti-TNF therapy. Toll-like receptor(TLR) expression and cytokine production post TLR stimulation was assessed in UC "responders"(n = 12) and "non-responders"(n = 12) and compared to healthy controls(n = 12). Erythrocyte sedimentation rate(ESR) and C-reactive protein(CRP) levels were measured in blood to assess disease severity/activity and inflammation. Pro-inflammatory(TNF, IL-1β, IL-6), immuno-regulatory(IL-10), Th1(IL-12, IFNγ) and Th2(IL-9, IL-13, IL-17A) cytokine expression was measured with enzyme-linked immunosorbent assay while TLR cellular composition and intracellular signalling was assessed with FACS.RESULTS Prior to anti-TNF therapy, responders and nonresponders had similar level of disease severity and activity. PBMC's ability to respond to TLR stimulation was not affected by TNF therapy, patient's severity of the disease and inflammation or their medication use. At baseline, non-responders had elevated innate but not adaptive immune responses compared to responders(P < 0.05). Following TLR stimulation, nonresponders had consistently reduced innate cytokine responses to all TLRs compared to healthy controls(P < 0.01) and diminished TNF(P < 0.001) and IL-1β(P < 0.01) production compared to responders. This innate immune dysfunction was associated with reduced number of circulating plasmacytoid dendritic cells(p DCs)(P < 0.01) but increased number of CD4+ regulatory T cells(Tregs)(P = 0.03) as well as intracellular accumulation of IRAK4 in non-responders following TLR-2,-4 and-7 activation(P < 0.001). CONCLUSION Reduced innate immunity in non-responders may explain reduced efficacy to anti-TNF therapy. These serological markers may prove useful in predicting the outcome of costly anti-TNF therapy.

P-glycoprotein multidrug transporter in inflammatory bowel diseases: More questions than answers

The gastrointestinal barrier is constantly exposed to numerous environmental substrates that are foreign and potentially harmful. These xenobiotics can cause shifts in the intestinal microbiota composition, affect mucosal immune responses, disturb tissue integrity and impair regeneration. The multidrug transporter ABCB1/MDR1 p-glycoprotein (p-gp) plays a key role at the front line of host defence by efficiently protecting the gastrointestinal barrier from xenobiotic accumulation. This Editorial discusses how altered expression and function of ABCB1/MDR1 p-gp may contribute to the development and persistence of chronic intestinal inflammation in inflammatory bowel diseases (IBD). Recent evidence implies multiple interactions between intestinal microbiota, innate immunity and xenobiotic metabolism via p-gp. While decreased efflux activity may promote disease susceptibility and drug toxicity, increased efflux activity may confer resistance to therapeutic drugs in IBD. Mice deficient in MDR1 A develop spontaneously chronic colitis, providing a highly valuable murine IBD model for the study of intestinal epithelial barrier function, immunoregulation, infectious co-triggers and novel therapeutic approaches. Possible associations of human ABCB1 gene polymorphisms with IBD susceptibility have been evaluated, but results are inconsistent. Future studies must focus on further elucidation of the pathophysiological relevance and immunological functions of p-gp and how its ambiguous effects could be therapeutically targeted in IBD.

Liver immunology and herbal treatment

Beyond the metabolic functions, the liver recently has been defined as an organ of immune system(IS), which have central regulatory role for innate and adaptive immunity. The liver keeps a delicate balance between hepatic screening of pathogenic antigens and immune tolerance to self-antigens. Herbal treatments with immunological effects have potential to alter this hepatic immune balance towards either therapeutic side or diseases side by inducing liver injury via hepatotoxicity or initiation of autoimmune diseases. Most commonly known herbal treatments, which have therapeutic effect on liver and IS, have proven via in vitro, in vivo, and/or clinical studies were summarized in this review.