CD100 up-regulation induced by interferon-α on B cells is related to hepatitis C virus infection

Recent Insights into the Role of B Cells in Chronic Hepatitis B and C Infections

Chronic viral hepatitis infections, caused by the hepatitis B or C virus, are a major global health problem causing an estimated one million deaths each year. Immunological studies have classically focused on T cells, while B cells have largely been neglected. Emerging evidence, however, highlights a role for B cells in the immunopathogenesis of chronic hepatitis B and C infections. B cell responses appear to be altered across different clinical phases of chronic HBV infection and across stages of disease in chronic HCV infection. These B cell responses show signs of a more activated state with a simultaneous enrichment of phenotypically exhausted atypical memory B cells. Despite the fact that studies show an activating B cell signature in chronic viral hepatitis infection, antibody responses to HBsAg remain impaired in chronic HBV infection, and glycoprotein E2-specific neutralizing antibody responses remain delayed in the acute phase of HCV infection. At the same time, studies have reported that a subset of HBV- and HCV-specific B cells exhibit an exhausted phenotype. This may, at least in part, explain why antibody responses in chronic HBV and HCV patients are suboptimal. Here, we summarize recent findings and discuss upcoming research questions while looking forward to how new single-cell technologies could provide novel insights into the role of B cells in chronic viral hepatitis infections.

Imbalance Between Soluble and Membrane-Bound CD100 Regulates Monocytes Activity in Hepatitis B Virus-Associated Acute-on-Chronic Liver Failure

CD100 is an important immune semaphorin that is a secreted and membrane bound protein involved in infectious diseases. However, CD100 expression profile and the regulation to innate immune system in hepatitis B virus (HBV)-associated acute-on-chronic liver failure (ACLF) was not previously reported. The aim of this study was to investigate CD100 level and modulatory function of CD100 to CD14⁺ monocytes in HBV-ACLF patients. Plasma-soluble CD100 (sCD100) level and membrane-bound CD100 (mCD100) expression on peripheral CD14⁺ monocytes was analyzed in HBV-ACLF patients. CD14⁺ monocytes-induced cytotoxicity and CD14⁺ monocytes-mediated T cell activation in response to CD100 stimulation was also assessed in direct and indirect contact coculture culture systems. HBV-ACLF patients had lower plasma sCD100 and higher mCD100 level on CD14⁺ monocytes compared with asymptomatic HBV carriers, chronic hepatitis B patients, and controls. CD14⁺ monocytes from HBV-ACLF patients induced limited target Huh7.5 cell death and secreted less interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and granzyme B in both direct and indirect contact coculture systems compared with controls. Recombinant sCD100 not only enhanced CD14⁺ monocytes-mediated Huh7.5 cell death and granzyme B secretion, but it also elevated CD14⁺ monocytes-induced IFN-γ/interleukin-17 production by CD4⁺ T cells as well as IFN-γ/TNF-α secretion by CD8⁺ T cells in HBV-ACLF patients. The current data indicated that severe inflammation induced sCD100/mCD100 imbalance to inactivate CD14⁺ monocytes response, which might be beneficial for the survival of HBV-ACLF patients.

MMP2/MMP9-mediated CD100 shedding is crucial for inducing intrahepatic anti-HBV CD8 T cell responses and HBV clearance

BACKGROUND & AIMS

CD100 is constitutively expressed on T cells and can be cleaved from the cell surface by matrix metalloproteases (MMPs) to become soluble CD100 (sCD100). Both membrane-bound CD100 (mCD100) and sCD100 have important immune regulatory functions that promote immune cell activation and responses. This study investigated the expression and role of mCD100 and sCD100 in regulating antiviral immune responses during HBV infection.

METHODS

mCD100 expression on T cells, sCD100 levels in the serum, and MMP expression in the liver and serum were analysed in patients with chronic HBV (CHB) and in HBV-replicating mice. The ability of sCD100 to mediate antigen-presenting cell maturation, HBV-specific T cell activation, and HBV clearance were analysed in HBV-replicating mice and patients with CHB.

RESULTS

Patients with CHB had higher mCD100 expression on T cells and lower serum sCD100 levels compared with healthy controls. Therapeutic sCD100 treatment resulted in the activation of DCs and liver sinusoidal endothelial cells, enhanced HBV-specific CD8 T cell responses, and accelerated HBV clearance, whereas blockade of its receptor CD72 attenuated the intrahepatic anti-HBV CD8 T cell response. Together with MMP9, MMP2 mediated mCD100 shedding from the T cell surface. Patients with CHB had significantly lower serum MMP2 levels, which positively correlated with serum sCD100 levels, compared with healthy controls. Inhibition of MMP2/9 activity resulted in an attenuated anti-HBV T cell response and delayed HBV clearance in mice.

CONCLUSIONS

MMP2/9-mediated sCD100 release has an important role in regulating intrahepatic anti-HBV CD8 T cell responses, thus mediating subsequent viral clearance during HBV infection.

LAY SUMMARY

Chronic hepatitis B virus (HBV) infection is a major public health problem worldwide. The clearance of HBV relies largely on an effective T cell immune response, which usually becomes dysregulated in chronic HBV infection. Our study provides a new mechanism to elucidate HBV persistence and a new target for developing immunotherapy strategies in patients chronically infected with HBV.

CD72/CD100 and PD-1/PD-L1 markers are increased on T and B cells in HIV-1+ viremic individuals, and CD72/CD100 axis is correlated with T-cell exhaustion

In our work, we analyzed the role of the CD100/CD72 and PD-1/PD-L1 axes in immune response dysfunction in human immunodeficiency virus (HIV)-1 infection in which high expressions of PD-1 and PD-L1 were associated with an immunosuppressive state via limitation of the HIV-1-specific T-cell responses. CD100 was demonstrated to play a relevant role in immune responses in various pathological processes and may be responsible for immune dysregulation during HIV-1 infection. We investigated the function of CD72/CD100, and PD-1/PDL-1 axes on T and B cells in HIV-infected individuals and in healthy individuals. We analyzed the frequencies and fluorescence intensities of these four markers on CD4+, CD8+ T and B cells. Marker expressions were increased during active HIV-1 infection. CD100 frequency on T cells was positively associated with the expression of PD-1 and PD-L1 on T cells from HIV-infected treatment-naïve individuals. In addition, the frequency of CD72-expressing T cells was associated with interferon gamma (IFN-γ) production in HIV-infected treatment-naïve individuals. Our data suggest that the CD72/CD100 and PD-1/PD-L1 axes may jointly participate in dysregulation of immunity during HIV-1 infection and could partially explain the immune systems' hyper-activation and exhaustion.

Low levels of the immunoregulator Semaphorin 4D (CD100) in sera of HIV patients

INTRODUCTION

Semaphorin-4D (CD100), generated by CD4/CD8 T-cells and its receptor on B cells - CD72, play a role in immune regulation. Both have soluble forms - sCD100/sCD72.

METHODS

sCD100 and sCD72 levels were determined by ELISA (MyBioSource, USA).

RESULTS

28 chronic HIV patients and 50 matched healthy volunteers participated in our study. Before treatment, CD4 T-cells counts were 267 ± 216 cells/mcl and viral load (VL) was 586,675 ± 1897,431 copies/ml. Two years following HAART, CD4 T-cells counts rose to 475 ± 264 cells/mcl and VL dropped to 2050 ± 10,539 copies/ml. CD8 T-cells counts were stable. sCD72 levels prior (4.13 ± 2.03 ng/ml) and following HAART (3.53 ± 2.01 ng/ml) were similar to control levels (4.51 ± 2.66 ng/ml). sCD100 levels before (40.47 ± 31.4 ng/ml) and following HAART (37.68 ± 29.44 ng/ml) were significantly lower compared to controls (99.67 ± 36.72 ng/ml) despite the significant increase in CD4 T-cells counts.

CONCLUSIONS

The permanent low levels of the immunoregulator sCD100 suggest a role for CD100 in the immune dysfunction and T cells exhaustion of HIV.

Interferon-α-induced CD100 on naïve CD8+ T cells enhances antiviral responses to hepatitis C infection through CD72 signal transduction

Objectives We investigated the effects of CD100 on naïve CD8⁺ T cells during hepatitis C virus (HCV) infection after interferon-α (IFN-α) therapy to clarify the mechanism underlying the effect of IFN-α in enhancing the antiviral response. Methods The CD100 molecules on subsets of CD8⁺ T cells were analysed with flow cytometry. The effects of CD100-overexpressing naïve CD8⁺ T cells were determined with ELISAs and an MTT cytotoxicity assay. The role of CD100-CD72 signal transduction was analysed with a neutralization and transwell assays. Results HCV infection reduced CD100 expression on CD8⁺ T cells, whereas IFN-α treatment significantly increased CD100 expression on naïve CD8⁺ T cells. The increased CD100 interacted with the CD72 receptor and enhanced PBMC cytokine secretion (IFN-γ and tumour necrosis factor-α) and cytotoxicity. Conclusions IFN-α-induced CD100 on naïve CD8⁺ T cells promotes PBMC cytokine secretion and cytotoxicity through CD100-CD72 signalling during HCV infection.

Soluble SEMA4D/CD100: A novel immunoregulator in infectious and inflammatory diseases

SEMA4D/CD100 is a homodimeric protein belonging to the semaphorin family of axonal guidance proteins. Semaphorin family members have received increased attention lately due to their diverse functions in the immune system. SEMA4D was the first semaphorin described to have immune functions and serves important roles in T cell priming, antibody production, and cell-to-cell adhesion. Proteolytic cleavage of SEMA4D from the cell surface gives rise to a soluble fragment of SEMA4D (sSEMA4D). Similar to the transmembranal form, sSEMA4D is thought to have immunoregulatory properties. While the exact mechanisms responsible for SEMA4D shedding remain to be elucidated, emerging data have revealed associations between elevated systemic sSEMA4D levels and severity of infectious and inflammatory diseases. This review summarizes the literature concerning sSEMA4D and discusses its potential as a novel prognostic immune-biomarker and potential target for immunotherapy.