title: Tim-3 negatively regulates IL-12 expression by monocytes in HCV infection.
abstract: T cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) is a newly identified negative immunomodulator that is up-regulated on dysfunctional T cells during viral infections. The expression and function of Tim-3 on human innate immune responses during HCV infection, however, remains poorly characterized. In this study, we report that Tim-3 is constitutively expressed on human resting CD14(+) monocyte/macrophages (M/M(Ø)) and functions as a cap to block IL-12, a key pro-inflammatory cytokine linking innate and adaptive immune responses. Tim-3 expression is significantly reduced and IL-12 expression increased upon stimulation with Toll-like receptor 4 (TLR4) ligand--lipopolysaccharide (LPS) and TLR7/8 ligand--R848. Notably, Tim-3 is over-expressed on un-stimulated as well as TLR-stimulated M/M(Ø), which is inversely associated with the diminished IL-12 expression in chronically HCV-infected individuals when compared to healthy subjects. Up-regulation of Tim-3 and inhibition of IL-12 are also observed in M/M(Ø) incubated with HCV-expressing hepatocytes, as well as in primary M/M(Ø) or monocytic THP-1 cells incubated with HCV core protein, an effect that mimics the function of complement C1q and is reversible by blocking the HCV core/gC1qR interaction. Importantly, blockade of Tim-3 signaling significantly rescues HCV-mediated inhibition of IL-12, which is primarily expressed by Tim-3 negative M/M(Ø). Tim-3 blockade reduces HCV core-mediated expression of the negative immunoregulators PD-1 and SOCS-1 and increases STAT-1 phosphorylation. Conversely, blocking PD-1 or silencing SOCS-1 gene expression also decreases Tim-3 expression and enhances IL-12 secretion and STAT-1 phosphorylation. These findings suggest that Tim-3 plays a crucial role in negative regulation of innate immune responses, through crosstalk with PD-1 and SOCS-1 and limiting STAT-1 phosphorylation, and may be a novel target for immunotherapy to HCV infection.
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee, United States of America.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.forename: Cheng J
authors.initials: CJ
authors.lastname: Ma
authors.forename: Jia M
authors.initials: JM
authors.lastname: Wang
authors.forename: Xiao J
authors.initials: XJ
authors.lastname: Ji
authors.forename: Xiao Y
authors.initials: XY
authors.lastname: Wu
authors.forename: Zhan S
authors.initials: ZS
authors.lastname: Jia
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Moorman
authors.forename: Zhi Q
authors.initials: ZQ
authors.lastname: Yao
mesh_terms: D000328:Adult; D015703:Antigens, CD / Q000378:metabolism; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D018920:Coculture Techniques; D015922:Complement C1q / Q000378:metabolism; D015536:Down-Regulation; D020868:Gene Silencing; D016174:Hepacivirus / Q000276:immunology*; D000072597:Hepatitis A Virus Cellular Receptor 2; D019698:Hepatitis C, Chronic / Q000276:immunology* / Q000821:virology; D022781:Hepatocytes / Q000378:metabolism / Q000821:virology; D006801:Humans; D053762:Interleukin-12 Subunit p40 / Q000096:biosynthesis / Q000378:metabolism*; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008262:Macrophage Activation / Q000276:immunology; D008264:Macrophages / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008875:Middle Aged; D024101:Mitochondrial Proteins / Q000378:metabolism; D009000:Monocytes / Q000378:metabolism*; D010766:Phosphorylation; D061026:Programmed Cell Death 1 Receptor; D011485:Protein Binding; D050794:STAT1 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics; D015854:Up-Regulation; D014758:Viral Core Proteins / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D051017:Apoptosis Regulatory Proteins; C087299:C1QBP protein, human; D002352:Carrier Proteins; C448908:HAVCR2 protein, human; D000072597:Hepatitis A Virus Cellular Receptor 2; C500879:IL12B protein, human; D053762:Interleukin-12 Subunit p40; D018950:Lipopolysaccharide Receptors; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C105992:PDCD1 protein, human; D061026:Programmed Cell Death 1 Receptor; C108944:SOCS1 protein, human; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus; D015922:Complement C1q