Induction of Profibrotic Microenvironment via TLR4 MyD88-Dependent and -Independent Inflammatory Signaling in Chronic Hepatitis C Virus Infection.

Hepatitis C virus (HCV) is a well-known pathogen to establish chronic infection leading to end-stage liver disease. The destruction of liver tissues takes its roots under chronic inflammation and proinflammatory signaling in liver microenvironment. The viral proteins interact with certain pattern recognition receptors, including Toll-like receptors, activating the innate immune system to clear the virus. HCV achieves immune evasion through other mechanisms and induce a continuous inflammatory microenvironment via Kupffer cells and Hepatic Stellate cells. This promotes disease progression. The current study aims to elucidate that the role of Toll-like receptor 4 (TLR4) induced innate immune response in chronic inflammation in patients chronically infected with HCV. For this purpose, changes in downstream signaling cascade of TLR4 during chronic HCV infection using peripheral blood mononuclear cells of chronic HCV patients were studied. We found significant increase in expression levels of proinflammatory and profibrotic genes induced by TLR4 Myeloid differentiation factor 88 (MyD88)-dependent pathway between treatment naive and healthy controls, while no significant difference between the expressions of genes involved in TLR4 signaling was found between treatment responders and healthy controls. Interestingly, both TLR4 MyD88-dependent and -independent pathways were found to be operational in nonresponders to interferon treatment. This further strengthens the involvement of innate immune signaling as a leading factor in HCV-mediated liver disease progression and the role of TLR4 MyD88-dependent and -independent pathway in ensuring the conditions for chronic inflammation.