Loss of CD4 T cell help correlates with virus persistence during acute hepatitis C virus (HCV) infection, but the underlying mechanism(s) remain unknown. We developed a combined proliferation/intracellular cytokine staining assay to monitor expansion of HCV-specific CD4 T cells and helper cytokines expression patterns during acute infections with different outcomes. We demonstrate that acute resolving HCV is characterized by strong Th1/Th17 responses with specific expansion of IL-21-producing CD4 T cells and increased IL-21 levels in plasma. In contrast, viral persistence was associated with lower frequencies of IL-21-producing CD4 T cells, reduced proliferation and increased expression of the inhibitory receptors T cell immunoglobulin and mucin-domain-containing-molecule-3 (Tim-3), programmed death 1 (PD-1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4) on HCV-specific CD8 T cells. Progression to persistent infection was accompanied by increased plasma levels of the Tim-3 ligand Galectin-9 (Gal-9) and expansion of Gal-9 expressing regulatory T cells (Tregs). In vitro supplementation of Tim-3high HCV-specific CD8 T cells with IL-21 enhanced their proliferation and prevented Gal-9 induced apoptosis. siRNA-mediated knockdown of Gal-9 in Treg cells rescued IL-21 production by HCV-specific CD4 T cells. We propose that failure of CD4 T cell help during acute HCV is partially due to an imbalance between Th17 and Treg cells whereby exhaustion of both CD4 and CD8 T cells through the Tim-3/Gal-9 pathway may be limited by IL-21 producing Th17 cells or enhanced by Gal-9 producing Tregs.

The majority of acute hepatitis C virus (HCV) infections progress to chronicity and progressive liver damage. Alpha interferon (IFN-␣) antiviral therapy achieves the highest rate of success when IFN-␣ is administered early during the acute phase, but the underlying mechanisms are unknown. We used a panel of major histocompatibility complex class I tetramers to monitor the phenotypic and functional signatures of HCVspecific T cells during acute HCV infection with different infection outcomes and during early IFN therapy. We demonstrate that spontaneous resolution correlates with the early development of polyfunctional (IFN-␥-and IL-2-producing and CD107a ؉ ) virus-specific CD8 ؉ T cells. These polyfunctional T cells are distinguished by the expression of CD127 and Bcl-2 and represent a transitional memory T-cell subset that exhibits the phenotypic and functional signatures of both central and effector memory T cells. In contrast, HCV-specific CD8 ؉ T cells in acute infections evolving to chronicity expressed low levels of CD127 and Bcl-2, exhibited diminished proliferation and cytokine production, and eventually disappeared from the periphery. Early therapeutic intervention with pegylated IFN-␣ rescued polyfunctional memory T cells expressing high levels of CD127 and Bcl-2. These cells were detectable for up to 1 year following discontinuation of therapy. Our results suggest that the polyfunctionality of HCV-specific T cells can be predictive of the outcome of acute HCV infection and that early therapeutic intervention can reconstitute the pool of long-lived polyfunctional memory T cells.Hepatitis C virus (HCV) infection resolves spontaneously during the acute phase in a minority of infected individuals while the majority develop persistent viremia and chronic hepatitis over a period of years or decades (28). Understanding the immune response leading to spontaneous resolution during acute HCV infection has been hampered by the asymptomatic nature of the disease. Studies in the chimpanzee model and high-risk populations like intravenous drug users (IDUs) or healthcare workers following HCV exposure have demonstrated the absolute requirement for the CD8 ϩ and CD4 ϩ HCV-specific T-cell responses to prevent viral persistence (reviewed in reference 12 and 50). A cellular immune response is induced in most infected individuals, resulting in spontaneous resolution or transient control of viremia. However, this response is not sustained in individuals who develop viral persistence. The inefficiency of this initial immune response and viral recurrence in individuals who progress to chronic infection are likely due to the loss of CD4 ϩ T-cell help (16,20,56,57) and the rapid emergence of viral escape mutants in targeted CD8 ϩ cytotoxic T lymphocyte epitopes (9). Individuals who spontaneously resolve HCV infection develop long-lived memory Tcell responses (54) that can be protective upon reexposure (51). In contrast, cellular immune responses are mostly undetectable in the blood of persistently infected individuals and are ...

Background/Aims-Natural killer (NK) cells provide early defense against viral infections by killing infected cells and producing cytokines that inhibit viral replication. NK cells also interact with dendritic cells (DCs) and this reciprocal interaction regulates both innate and adaptive immunity. Genetic studies have suggested that NK cell activity is a determinant of HCV infectious outcome but a functional correlation was not established. We hypothesized that increased NK cell activity during acute HCV infection will correlate with spontaneous viral clearance.

Activation of AMPK has been associated with pro‐atrophic signaling in muscle. However, AMPK also has anti‐inflammatory effects, suggesting that in cachexia, a syndrome of inflammatory‐driven muscle wasting, AMPK activation could be beneficial. Here we show that the AMPK agonist AICAR suppresses IFNγ/TNFα‐induced atrophy, while the mitochondrial inhibitor metformin does not. IFNγ/TNFα impair mitochondrial oxidative respiration in myotubes and promote a metabolic shift to aerobic glycolysis, similarly to metformin. In contrast, AICAR partially restored metabolic function. The effects of AICAR were prevented by the AMPK inhibitor Compound C and were reproduced with A‐769662, a specific AMPK activator. AICAR and A‐769662 co‐treatment was found to be synergistic, suggesting that the anti‐cachectic effects of these drugs are mediated through AMPK activation. AICAR spared muscle mass in mouse models of cancer and LPS induced atrophy. Together, our findings suggest a dual function for AMPK during inflammation‐driven atrophy, wherein it can play a protective role when activated exogenously early in disease progression, but may contribute to anabolic suppression and atrophy when activated later through mitochondrial dysfunction and subsequent metabolic stress.