Infection with hepatitis C virus (HCV) is associated with persistence in the majority of individuals. We demonstrate here that the inhibitory molecule programmed death-1 (PD-1) is significantly upregulated on total and HCV-specific CD8 ؉ cytotoxic T lymphocytes (CTLs) in the peripheral blood and livers of patients with chronic infection compared to subjects with spontaneous HCV resolution, patients with nonviral liver disease, and normal controls. PD-1 expression on cytomegalovirus-specific CTLs also varies according to HCV status and is highest in patients with chronic infection. HCV-specific CTLs that are PD-1 high express higher levels of the senescence marker CD57 than PD-1 low CTLs, and CD57 expression is greater in chronic than in resolved infection. In vitro blockade of PD-1 by monoclonal antibodies specific to its ligands (PD-L1 and PD-L2) results in restoration of functional competence (proliferation and gamma interferon and interleukin-2 secretion) of HCV-specific CTLs, including those residing in the liver. This reversal of CTL exhaustion is evident even in individuals who lack HCV-specific CD4 ؉ T-cell help. Our data indicate that the PD-1/PD-L pathway is critical in persistent HCV infection in humans and represents a potential novel target for restoring function of exhausted HCV-specific CTLs. Hepatitis C virus (HCV) is the major causative agent of chronic hepatitis and has an estimated global prevalence of 3% (31). It is not precisely understood why the majority of individuals exposed to HCV develop viral persistence and only a minority experience spontaneous resolution. Moreover, antiviral therapy is effective in only about half of chronically infected patients, and those who fail antiviral therapy are at increased risk of disease progression, including development of cirrhosis and end-stage liver disease (17). Chronic HCV infection is manifested by cytotoxic T lymphocytes (CTLs) that are functionally impaired or exhausted (decreased antiviral cytokine production, cytotoxicity, and proliferative capacity) (15,30) and may exhibit phenotypic features of early stages of differentiation (1, 18). Recent reports indicate that PD-1 is markedly upregulated on surface of exhausted virus-specific CD8 ϩ T cells in mice with lymphocytic choriomeningitis virus (3) and in humans with human immunodeficiency virus (HIV) infection (8,24,28), and emerging data indicate a significant role for this immunoreceptor in HCV infection (23,25,29). In this regard, hepatic expression of PD-1 mRNA recently was shown to be increased in four acutely infected chimpanzees that subsequently developed persistence in contrast to lower levels in the two animals who spontaneously resolved HCV (26).In the present study, we report the expression of PD-1 on bulk and HCV-specific CTLs from patients with chronic infection and subjects with spontaneous recovery, as well as the consequences of manipulating PD-1/PD-L pathway on proliferation and effector cytokine production by these cells. We find that PD-1 is markedly upregulated in the peri...

Non-alcoholic fatty liver disease (NAFLD), a common prelude to cirrhosis and hepatocellular carcinoma, is the most common chronic liver disease worldwide. Defining the molecular mechanisms underlying the pathogenesis of NAFLD has been hampered by a lack of animal models that closely recapitulate the severe end of the human disease spectrum, including bridging hepatic fibrosis. Here, we demonstrate that a novel experimental model employing thermoneutral housing, as opposed to standard housing, resulted in lower stress-driven production of corticosterone, augmented mouse proinflammatory immune responses and markedly exacerbated high fat diet (HFD)-induced NAFLD pathogenesis. Disease exacerbation at thermoneutrality was conserved across multiple mouse strains and was associated with augmented intestinal permeability, an altered microbiome and activation of inflammatory pathways associated with human disease. Depletion of Gram-negative microbiota, hematopoietic cell deletion of Toll-like receptor 4 (TLR4) and inactivation of the interleukin-17 (IL-17) axis resulted in altered immune responsiveness and protection from thermoneutral housing-driven NAFLD amplification. Finally, female mice, typically resistant to HFD-induced obesity and NAFLD, develop full-blown disease at thermoneutrality. Thus, thermoneutral housing provides a sex-independent model of exacerbated NAFLD in mice and represents a novel approach for interrogation of the cellular and molecular mechanisms underlying disease pathogenesis.

Summary In human vitiligo, cutaneous depigmentation involves cytotoxic activity of autoreactive T cells. It was hypothesized that depigmentation can progress in the absence of regulatory T cells (Treg). The percentage of Treg among skin infiltrating T cells was evaluated by immunoenzymatic double staining for CD3 and FoxP3, revealing drastically reduced numbers of Treg in non-lesional, perilesional and lesional vitiligo skin. Assessment of the circulating Treg pool by FACS analysis of CD4, CD25, CD127 and FoxP3 expression, and mixed lymphocyte reactions in presence and absence of sorted Treg revealed no systemic drop in the abundance or activity of Treg in vitiligo patients. Expression of skin homing receptors CCR4, CCR5, CCR8 and CLA was comparable among circulating vitiligo and control Treg. Treg from either source were equally capable of migrating towards CCR4 ligand and skin homing chemokine CCL22, yet significantly reduced expression of CCL22 in vitiligo skin observed by immunohistochemistry may explain failure of circulating, functional Treg to home to the skin in vitiligo. The paucity of Treg in vitiligo skin is likely crucial for perpetual anti-melanocyte reactivity in progressive disease.