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

Soluble Semaphorin 4D Serum Concentrations Are Elevated in Critically Ill Patients with Liver Cirrhosis and Correlate with Aminotransferases

Semaphorin 4D (Sema4D), also known as CD100, is a multifunctional transmembrane protein with immunoregulatory functions. Upon the activation of immune cells, soluble Semaphorin 4D (sSema4D) is proteolytically cleaved from the membrane by metalloproteinases. sSema4D levels are elevated in various (auto-)inflammatory diseases. Our aim was to investigate sSema4D levels in association with sepsis and critical illnesses and to evaluate sSema4D's potential as a prognostic biomarker. We measured sSema4D levels in 192 patients upon admission to our medical intensive care unit. We found similar levels of sSema4D in 125 patients with sepsis compared to 67 non-septic patients. sSema4D levels correlated with leukocytes but not with other markers of systemic inflammation such as C-reactive protein or procalcitonin. Most interestingly, in a subgroup of patients suffering from pre-existing liver cirrhosis, we observed significantly higher levels of sSema4D. Consistently, sSema4D was also positively correlated with markers of hepatic and cholestatic injury. Our study suggests that sSema4D is not regulated in sepsis compared to other causes of critical illness. However, sSema4D seems to be associated with hepatic injury and inflammation.

Tenofovir Modulates Semaphorin 4D Signaling and Regulates Bone Homeostasis, Which Can Be Counteracted by Dipyridamole and Adenosine A2A Receptor

Semaphorin 4D (Sema4D) is a neurotrophin that is secreted by osteoclasts and binds to its receptor PlexinB1 on osteoblasts to inhibit their differentiation and function. Adenosine A2A activation inhibits osteoclast Sema4D-mediated secretion, diminishes inflammatory osteolysis and prevents bone loss following tenofovir (one of the most used antivirals in HIV). Therefore, tenofovir might activate Sema4D signaling to alter bone turnover. Female C57Bl/6/A2AKO mice were ovariectomized and treated with saline (control), tenofovir 75 mg/Kg/day, dipyridamole 25 mg/Kg/day or a combination for 5 weeks and long bones were prepared for histology. Primary murine-induced osteoclast/osteoblast were challenged with tenofovir/dipyridamole 1 μM each, and the expression of Sema4D/PlexinB1, RhoA/ROCK/IGF1R was studied by RT-PCR, Western blot and immunostaining. In vivo tenofovir showed an increased expression of Sema4D when compared to control mice, and dipyridamole reverted the expression in an A2A-dependent manner. In vitro, tenofovir increases Sema4D expression and secretion in osteoclast precursors, and pre-treatment with dipyridamole reverted this effect. pRhoA and ROCK1 activation were increased and IRS1/IGF1R expression was diminished by tenofovir in the Vav3/ARHGAP18 mechanism in osteoblast precursors and reverted by dipyridamole in an A2A-dependent manner. This suggests that tenofovir increases bone loss by activation of Sema4D/PlexinB1 signaling, which inhibits osteoblast differentiation. Agents that increase local adenosine concentrations, such as dipyridamole, might prevent bone loss following the inhibition of this pathway.

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.

CD100 modulates cytotoxicity of CD8+ T cells in patients with acute myocardial infarction

BACKGROUND

CD100 is an immune semaphorin family member that highly expressed on T cells, which take part in the development of acute myocardial infarction (AMI). Matrix metalloproteinases (MMPs) are important mediators for membrane-bound CD100 (mCD100) shedding from T cells to generate soluble CD100 (sCD100), which has immunoregulatory effect on T cells. The aim of this study was to investigate modulatory role of CD100 on CD8⁺ T cell activity in AMI patients.

METHODS

Peripheral sCD100 and MMP-2 level, as well as mCD100 level on T cells was assessed in patients with stable angina pectoris (SAP), unstable angina pectoris (UAP), and AMI. The regulatory function of MMP-2 on mCD100 shedding, sCD100 formation, and cytotoxicity of CD8⁺ T cells was analyzed in direct and indirect contact co-culture system.

RESULTS

AMI patients had higher peripheral sCD100 and lower mCD100 expression on CD8⁺ T cells in comparison with SAP, UAP, and controls. CD8⁺ T cells in AMI patients showed elevated direct cytotoxicity, enhanced cytokine production, and increased perforin/granzyme B secretion. Recombinant sCD100 stimulation promoted cytolytic function of CD8⁺ T cells in controls and AMI patients. Furthermore, AMI patients also had elevated circulating MMP-2 level. Recombinant MMP-2 stimulation induced mCD100 shedding from CD8⁺ T cells and sCD100 generation, resulting in enhancement of CD8⁺ T cell cytotoxicity in AMI patients.

CONCLUSION

Up-regulation of MMP-2 might contribute to elevation of mCD100 shedding and sCD100 formation, leading to increased cytotoxicity CD8⁺ T cells in AMI patients.

HIV-1 infection activates endogenous retroviral promoters regulating antiviral gene expression

Although endogenous retroviruses (ERVs) are known to harbor cis-regulatory elements, their role in modulating cellular immune responses remains poorly understood. Using an RNA-seq approach, we show that several members of the ERV9 lineage, particularly LTR12C elements, are activated upon HIV-1 infection of primary CD4⁺ T cells. Intriguingly, HIV-1-induced ERVs harboring transcription start sites are primarily found in the vicinity of immunity genes. For example, HIV-1 infection activates LTR12C elements upstream of the interferon-inducible genes GBP2 and GBP5 that encode for broad-spectrum antiviral factors. Reporter assays demonstrated that these LTR12C elements drive gene expression in primary CD4⁺ T cells. In line with this, HIV-1 infection triggered the expression of a unique GBP2 transcript variant by activating a cryptic transcription start site within LTR12C. Furthermore, stimulation with HIV-1-induced cytokines increased GBP2 and GBP5 expression in human cells, but not in macaque cells that naturally lack the GBP5 gene and the LTR12C element upstream of GBP2. Finally, our findings suggest that GBP2 and GBP5 have already been active against ancient viral pathogens as they suppress the maturation of the extinct retrovirus HERV-K (HML-2). In summary, our findings uncover how human cells can exploit remnants of once-infectious retroviruses to regulate antiviral gene expression.

Insufficient CD100 shedding contributes to suppression of CD8+ T-cell activity in non-small cell lung cancer

CD100 is an immune semaphorin constitutively expressed on T-cells. Matrix metalloproteinase (MMP) is an important mediator of membrane-bound CD100 (mCD100) cleavage to generate soluble CD100 (sCD100), which has immunoregulatory activity in immune cell responses. The aim of the study was to investigate the level and role of sCD100 and mCD100 in modulating CD8⁺ T-cell function in non-small cell lung cancer (NSCLC). sCD100 and MMP-14 levels in the serum and bronchoalveolar lavage fluid (BALF), and mCD100 expression on peripheral and lung-resident CD8⁺ T-cells were analysed in NSCLC patients. The ability to induce sCD100 and the effect of MMP-14 on mCD100 shedding for the regulation of non-cytolytic and cytolytic functions of CD8⁺ T-cells were also analysed in direct and indirect contact co-culture systems. NSCLC patients had lower serum sCD100 and higher mCD100 levels on CD8⁺ T-cells compared with healthy controls. BALF from the tumour site also had decreased sCD100 and increased mCD100 on CD8⁺ T-cells compared with the non-tumour site. Recombinant CD100 stimulation enhanced non-cytolytic and cytolytic functions of CD8⁺ T-cells from NSCLC patients, whereas blockade of CD100 receptor CD72 attenuated CD8⁺ T-cell activity. NSCLC patients had lower MMP-14 in the serum and in BALF from the tumour site. Recombinant MMP-14 mediated mCD100 shedding from CD8⁺ T-cell membrane, and led to promotion of CD8⁺ T-cell response in NSCLC patients. Overall, decreased MMP-14 resulted in insufficient CD100 shedding, leading to suppression of peripheral and lung-resident CD8⁺ T-cell activity in NSCLC.

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.