Barathan, Muttiah (2016) Studies on immune impairment in chronic Hepatitis C virus infection / Barathan Muttiah. Masters thesis, University of Malaya.
Abstract
Hepatitis C virus (HCV) is a blood-borne pathogen that infects hepatocytes and causes widespread destruction to the host immune system. Estimates suggest that HCV has infected ~200 million people worldwide, and ~350,000-500,000 people die every year from HCV-associated hepatic and extra-hepatic complications. HCV has developed numerous mechanisms to evade host immune responses to establish persistence. Due to the lack of a preventive vaccine, the mainstay of current treatment is a combination therapy with interferon-α and ribavirin. The molecular mechanisms underlying the establishment of persistent HCV disease remain poorly understood. A better understanding of these mechanisms would aid design newer therapeutic targets and improve the quality of life of HCV-infected patients Here, we aimed to investigate the role of spontaneous apoptosis of immune cells, expansion of senescent and exhausted virus-specific T-cells, as well as potential depletion of circulating mucosal-associated invariant T (MAIT) cells, with immune impairment in chronic HCV (CHC) disease. We recruited 62 chronically-infected HCV patients and 62 healthy controls (HCs) to conduct a cross-sectional investigation. Peripheral blood mononuclear cells (PBMCs) were isolated, and co-cultured with HCV antigens and phytohaemagglutinin (PHA) individually prior to the investigations (except for apoptosis). Flow cytometry, quantitative real-time PCR (qRT-PCR), ELISA and QuantiGene Plex 2.0 analyses were employed to investigate apoptosis in immune cells. Multiparametric flow cytometry approaches were utilized to examine the phenotypes of immunosenescent T-cells and expression of co-inhibitory molecules on HCV-specific T cells, together with frequencies of circulating MAIT cells. Expression of molecules associated with T-cell inhibition was confirmed by qRT-PCR. iv The ability of HCV to induce apoptosis in immune cells correlated with the increase of apoptotic cells (Annexin V+PI+) and cellular reactive oxygen species (ROS). QuantiGene Plex 2.0 analysis showed differential regulation of apoptotic pathways involved in mitochondrial or activation of death receptors. Besides, the onset of immunosenescence was clearly evident from the up-regulation of HLA-DR, CD38, CD57 and CD127 on HCV-specific CD4+ and CD8+ T-cells of chronic HCV-infected patients. Furthermore, chronic HCV-infected patients displayed relatively significant increase of late-differentiated T-cells. Chronic HCV infection also resulted in significantly increased expressions of PD-1, CTLA-4, CD160 and TRAIL on HCV-specific CD4+ and CD8+ T cells suggestive of immune exhaustion. Increase in the levels of pro-inflammatory cytokines was also observed in PBMC cultures of chronic HCV-infected patients. MAIT cells of HCs expressed elevated levels of CCR5 and CCR6. Conversely, all these receptors were down-regulated on the circulating MAIT cells of chronic HCV-infected patients. Expression of PD-1 was also higher on MAIT cells of chronic HCV-infected patients relative to controls. In conclusion, our observation suggests the spontaneous onset of apoptosis signaling in chronic HCV disease, and increased frequency of late-senescent T-cells that lack the potential to survive, possibly contributing to viral persistence. These phenotypically defective HCV-specific T-cells may likely contribute to inadequate virus-specific T-cell responses. Decreased frequency of MAIT cells with elevated levels of PD-1 may result in diminished mucosal defense attributes, and could potentially contribute to HCV disease progression.
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