Proteolytic degradation of articular cartilage is a hallmark of osteoarthritic (OA) joint destruction. Articular cartilage contains chondrocytes embedded in an avascular matrix composed primarily of type II collagen (CII) fibrils and the proteoglycan, aggrecan. Collagen fibrils provide tensile strength and serve as a lattice to anchor water-laden proteoglycans, which deform while absorbing impact loads (1). OA chondrocytes and the adjacent synovial tissue secrete the inflammatory cytokine interleukin-1␤ (IL-1␤), which stimulates chondrocytes to secrete neutral proteases that degrade both collagen and proteoglycans (2,3). The newly cloned aggrecanase (4) and multiple matrix metalloproteinases (MMP) are secreted (5) and cleave aggrecan, the predominant proteoglycan, while other MMP known as the collagenases are the only enzymes able to degrade CII. MMPs are a family of zinc-containing, calciumdependent neutral proteases that share a common domain structure. Collectively these enzymes can degrade the components of the extracellular matrix (6,7).

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...

Approximately 200 million people throughout the world are infected with hepatitis C virus (HCV). One of the most striking features of HCV infection is its high propensity to establish persistence (∼70–80%) and progressive liver injury. Galectins are evolutionarily conserved glycan-binding proteins with diverse roles in innate and adaptive immune responses. Here, we demonstrate that galectin-9, the natural ligand for the T cell immunoglobulin domain and mucin domain protein 3 (Tim-3), circulates at very high levels in the serum and its hepatic expression (particularly on Kupffer cells) is significantly increased in patients with chronic HCV as compared to normal controls. Galectin-9 production from monocytes and macrophages is induced by IFN-γ, which has been shown to be elevated in chronic HCV infection. In turn, galectin-9 induces pro-inflammatory cytokines in liver-derived and peripheral mononuclear cells; galectin-9 also induces anti-inflammatory cytokines from peripheral but not hepatic mononuclear cells. Galectin-9 results in expansion of CD4+CD25+FoxP3+CD127low regulatory T cells, contraction of CD4+ effector T cells, and apoptosis of HCV-specific CTLs. In conclusion, galectin-9 production by Kupffer cells links the innate and adaptive immune response, providing a potential novel immunotherapeutic target in this common viral infection.

Osteoarthritic chondrocytes secrete matrix metalloproteinase-13 (MMP-13) in response to interleukin-1 (IL-1), causing digestion of type II collagen in cartilage. Using chondrocytic cells, we previously determined that IL-1 induced a strong MMP-13 transcriptional response that requires p38 MAPK, JNK and the transcription factor NF-kappaB. Now, we have studied the tissue-specific transcriptional regulation of MMP-13. Constitutive expression of the transcription factor Runx-2 correlated with the ability of a cell type to express MMP-13 and was required for IL-1 induction; moreover, Runx-2 enhanced IL-1 induction of MMP-13 transcription by synergizing with the p38 MAPK signaling pathway. Transiently transfected MMP-13 promoters were not IL-1 inducible. However, -405 bp of stably integrated promoter was sufficient for 5- to 6-fold IL-1 induction of reporter activity and this integrated reporter required the same p38 MAPK pathway as the endogenous gene. Finally, mutation of the proximal Runx binding site and the proximal AP-1 site blunted the transcriptional response to IL-1, and double mutation synergistically decreased reporter activity. In summary, our data suggest that the transcriptional MMP-13 response to IL-1 is controlled by the p38 pathway interacting at the MMP-13 promoter through the tissue-specific transcription factor Runx-2 and the ubiquitous AP-1 transcription factor.