Phenotypic and functional changes of cytotoxic CD56pos natural T cells determine outcome of acute hepatitis C virus infection

Hepatitis C virus versus innate and adaptive immune responses: a tale of coevolution and coexistence

Since the identification of the hepatitis C virus (HCV) 20 years ago, much progress has been made in our understanding of its life cycle and interaction with the host immune system. Much has been learned from HCV itself, which, via decades of coevolution, gained an intricate knowledge of host innate and adaptive immune responses and developed sophisticated ways to preempt, subvert, and antagonize them. This review discusses the clinical, virological, and immunological features of acute and chronic hepatitis C and the role of the immune response in spontaneous and treatment-induced HCV clearance.

CD56+ T cells inhibit hepatitis C virus replication in human hepatocytes

CD56(+) T cells are abundant in liver and play an important role in defense against viral infections. However, the role of CD56(+) T cells in control of hepatitis C virus (HCV) infection remains to be determined. We investigated the noncytolytic anti-HCV activity of primary CD56(+) T cells in human hepatocytes. When HCV Japanese fulminant hepatitis-1 (JFH-1)-infected hepatocytes were co-cultured with CD56(+) T cells or incubated in media conditioned with CD56(+) T cell culture supernatants (SN), HCV infectivity and replication were significantly inhibited. The antibodies to interferon (IFN)-gamma or IFN-gamma receptor could largely block CD56(+) T cell-mediated anti-HCV activity. Investigation of mechanism(s) responsible for CD56(+) T cell-mediated noncytolytic anti-HCV activity showed that CD56(+) T SN activated the multiple elements of janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway and enhanced the expression of IFN regulatory factors (IRFs) 1, 3, 7, 8, and 9, resulting in the induction of endogenous IFN-alpha/beta expression in hepatocytes. Moreover, CD56(+) T SN treatment inhibited the expression of HCV-supportive micro RNA (miRNA)-122 and enhanced the levels of anti-HCV miRNA-196a in human hepatocytes.

CONCLUSION

These findings provide direct in vitro evidence at cellular and molecular levels that CD56(+) T cells may have an essential role in innate immune cell-mediated defense against HCV infection. (HEPATOLOGY 2009.).

A novel role for adiponectin in regulating the immune responses in chronic hepatitis C virus infection

Adipose tissue releases pro-inflammatory and anti-inflammatory mediators, including adiponectin, which elicit a broad range of metabolic and immunological effects. The study aim was to determine in subjects infected with chronic hepatitis C virus (HCV) the effects of total adiponectin and its high-molecular-weight (HMW) and low-molecular-weight isoforms on HCV-specific immune responses. Serum levels of total adiponectin and its isoforms were determined by immunoassay. The ex vivo effect of adiponectin on the HCV-specific T-cell response was examined by interferon gamma (IFN-gamma) enzyme-linked immunosorbent spot and enzyme-linked immunosorbent assay cytokine assays. The role of the mitogen-activated protein kinase (MAPK) signaling pathway in mediating the adiponectin effect on T cells was also evaluated. We found that serum levels of total and HMW adiponectin were significantly decreased in subjects with chronic HCV and increased body mass index (BMI) compared with HCV-infected lean subjects. The presence of an anti-HCV specific immune response was strongly associated with lower BMI (P = 0.004) and higher serum total (P = 0.01) and HMW (P = 0.02) adiponectin. In ex vivo assays, total adiponectin and the HMW adiponectin isoform enhanced HCV-specific IFN-gamma production (P = 0.02 and 0.03, respectively). Adiponectin-R1 receptors were expressed on T cells and monocytes. In depletion experiments, the IFN-gamma response to adiponectin was entirely dependent on the simultaneous presence of both CD4 and CD8 T cells, and to a lesser extent, natural killer cells. Selective inhibition of p38MAPK activity by SB203580 abrogated the IFN-gamma response to adiponectin, whereas extracellular signal-regulated kinase 1/2 inhibition by PD98059 did not affect the response.

CONCLUSION

In chronic HCV, a reciprocal association exists between BMI, adiponectin, and the anti-HCV immune responses, emphasizing the important role played by adiposity in regulating the immune response in HCV infection.