Hongxiao Song

Hepatitis C virus core protein triggers expansion and activation of CD4+CD25+regulatory T cells in chronic hepatitis C patients

CD4+CD25+FoxP3+ regulatory T cells (Tregs) are increased in patients with chronic hepatitis C, which may contribute to the sustained suppression of hepatitis C virus (HCV)-specific T-cell responses and viral persistence in HCV-infected individuals. We postulated that HCV core protein (HCVc) directly contributes to the expansion of Tregs in HCV-infected patients, and we provide evidence to support this hypothesis in the report. Peripheral blood mononuclear cells (PBMCs) and sera were collected from 87 treatment-naïve chronic HCV-infected patients, CD4+CD25+ Tregs were measured by flow cytometry, and HCV RNA and HCVc levels were detected using qPCR and enzyme-linked immunosorbent assay (ELISA), respectively. CD4+, CD8+, CD4+CD25+ and CD4+CD25− T cells were purified from healthy donors and cultured with recombinant HCVc and Toll-like receptor (TLR) ligands. Flow cytometry was used to analyze cell proliferation, and ELISA was performed to measure cytokine production. In the 87 chronic HCV-infected patients, HCVc showed a significant correlation with HCV RNA and CD4+CD25+ Tregs. Mechanistic studies showed that HCVc, together with anti-CD3 antibody, augmented CD4+CD25+ Treg proliferation, but inhibited CD4+CD25− T-cell proliferation and IFN-γ production, in a dose-dependent and Treg-dependent manner. Moreover, unlike the TLR3 ligand (poly I:C) and the TLR4 ligand (lipopolysaccharide, LPS), the TLR2 ligand (lipoteichoic acid, LTA) and HCVc both inhibited TCR-induced CD4+ T-cell proliferation and IFN-γ secretion in a Treg-dependent manner. These data indicate that HCVc, like other TLR2 ligands, triggers CD4+CD25+ Treg activation and expansion to inhibit host immune responses, which may play a critical role in viral persistence in HCV-infected patients.

Hepatitis C virus induces MDSCs-like monocytes through TLR2/PI3K/AKT/STAT3 signaling

Background and Aims Recent studies reveal the accumulation of myeloid derived suppressor cells (MDSCs) in human peripheral blood mononuclear cells (PBMCs) following HCV infection, which may facilitate and maintain HCV persistent infection. The mechanisms by which HCV induces MDSCs are poorly understood. In the present study, we investigated the mechanisms by which HCV induces MDSCs that lead to suppression of T cell proliferation and expansion of CD4+Foxp3+ regulatory T cells. Methods Purified monocytes from healthy donors were cultured with HCV core protein (HCVc) or cell culture-derived HCV virions (HCVcc), and characterized the phenotype and function of these monocytes by flow cytometry, quantitative PCR, ELISA and western blot assays. In addition, peripheral blood from healthy donors and chronic HCV infected patients was collected, and MDSCs and CD4+CD25+CD127- regulatory T cells were analyzed by flow cytometry. Results Both HCVc and HCVcc induced expression of IDO1, PD-L1 and IL-10, and significantly down-regulated HLA-DR expression in human monocytes. HCVc-treated monocytes triggered CD4+Foxp3+ Tregs expansion, and inhibited autologous CD4+ T cell activation in an IDO1-dependent fashion. Our results showed that HCV virions or HCV core proteins induced MDSC-like suppressive monocytes via the TLR2/PI3K/AKT/STAT3 signaling pathway. Monocytes derived from patients with chronic HCV infection displayed MDSCs characteristics. Moreover, the percentages of CD14+ MDSCs and CD4+CD25+CD127- Tregs in chronic HCV infected patients were significantly higher than healthy individuals, and the frequency of MDSCs correlated with CD4+CD25+CD127- Tregs. Conclusions HCV induced MDSC-like suppressive monocytes through TLR2/PI3K/AKT/STAT3 signaling pathway to induce CD4+Foxp3+ regulatory T cells and inhibit autologous CD4+ T cell activation. It will be of interest to test whether antagonizing suppressive functions of MDSCs could enhance immune responses and virus control in chronic HCV infection.

Hepatitis C virus regulates the production of monocytic myeloid-derived suppressor cells from peripheral blood mononuclear cells through PI3K pathway and autocrine signaling.

Hepatitis C virus (HCV) infection is a major liver disease that ultimately develops into chronic hepatitis. Consequently, such patients are predisposed to serious complications, such as hepatocellular carcinoma. In HCV-infected patients, impaired T-cell responses are associated with persistent infection. Myeloid-derived suppressor cells (MDSCs) play a pivotal role in suppressing T-cell responses. In this study, we investigated the capacity and mechanism through which HCV transforms CD14+ monocytes into monocytic (Mo)-MDSCs. We showed that HCV core protein promotes CD14+ monocytes to develop a CD14+HLA-DR/low phenotype with upregulated indoleamine 2,3-dioxygenase (IDO) expression and suppressed T-cell proliferation. Importantly, HCV-induced Mo-MDSC production was attributed to the PI3K pathway via induction of IL-10 and TNF-α secretion. This process could be reversed by polyinosinic:polycytidylic acid (polyI:C) treatment. In conclusion, our results suggest that HCV regulates Mo-MDSC production from monocytes through the PI3K pathway and autocrine cytokines. The latter can serve as effective targets for novel HCV therapies.

The Role of Immune Cells in Chronic HBV Infection

Hepatitis B virus (HBV) infection is a major cause of chronic liver diseases that may progress to liver cirrhosis and hepatocellular carcinoma. Host immune responses are important factors that determine whether HBV infection is cleared or persists. After infection, viral replication occurs inside hepatocytes, and the secretion of infectious virions can take place at high rates for decades. Consequently, HBV DNA and viral proteins, like HBV early antigen (HBeAg) and HBV surface antigen (HBsAg), can be easily detected in serum. Chronic infection with HBV is the result of an ineffective antiviral immune response towards the virus. In this review, we discuss the role of immune cells in chronic HBV infection.

Regulatory NK cells mediated between immunosuppressive monocytes and dysfunctional T cells in chronic HBV infection

Background and aims HBV infection represents a major health problem worldwide, but the immunological mechanisms by which HBV causes chronic persistent infection remain only partly understood. Recently, cell subsets with suppressive features have been recognised among monocytes and natural killer (NK) cells. Here we examine the effects of HBV on monocytes and NK cells. Methods Monocytes and NK cells derived from chronic HBV-infected patients and healthy controls were purified and characterised for phenotype, gene expression and cytokines secretion by flow cytometry, quantitative real-time (qRT)-PCR, ELISA and western blotting. Culture and coculture of monocytes and NK cells were used to determine NK cell activation, using intracellular cytokines staining. Results In chronic HBV infection, monocytes express higher levels of PD-L1, HLA-E, interleukin (IL)-10 and TGF-β, and NK cells express higher levels of PD-1, CD94 and IL-10, compared with healthy individuals. HBV employs hepatitis B surface antigen (HBsAg) to induce suppressive monocytes with HLA-E, PD-L1, IL-10 and TGF-β expression via the MyD88/NFκB signalling pathway. HBV-treated monocytes induce NK cells to produce IL-10, via PD-L1 and HLA-E signals. Such NK cells inhibit autologous T cell activation. Conclusions Our findings reveal an immunosuppressive cascade, in which HBV generates suppressive monocytes, which initiate regulatory NK cells differentiation resulting in T cell inhibition.

HCV core protein inhibits polarization and activity of both M1 and M2 macrophages through the TLR2 signaling pathway

Hepatitis C virus (HCV) establishes persistent infection in most infected patients, and eventually causes chronic hepatitis, cirrhosis, and hepatocellular carcinoma in some patients. Monocytes and macrophages provide the first line of defense against pathogens, but their roles in HCV infection remains unclear. We have reported that HCV core protein (HCVc) manipulates human blood-derived dendritic cell development. In the present study, we tested whether HCVc affects human blood-derived monocyte differentiating into macrophages. Results showed that HCVc inhibits monocyte differentiation to either M1 or M2 macrophages through TLR2, associated with impaired STATs signaling pathway. Moreover, HCVc inhibits phagocytosis activity of M1 and M2 macrophages, M1 macrophage-induced autologous and allogeneic CD4+ T cell activation, but promotes M2 macrophage-induced autologous and allogeneic CD4+ T cell activation. In conclusion, HCVc inhibits monocyte-derived macrophage polarization via TLR2 signaling, leading to dysfunctions of both M1 and M2 macrophages in chronic HCV infected patients. This may contribute to the mechanism of HCV persistent infection, and suggest that blockade of HCVc might be a novel therapeutic approach to treating HCV infection.

IL-10 plays a central regulatory role in the cytokines induced by hepatitis C virus core protein and polyinosinic acid:polycytodylic acid.

Hepatitis C virus (HCV) can cause persistent infection and chronic liver disease, and viral factors are involved in HCV persistence. HCV core protein, a highly conserved viral protein, not only elicits an immunoresponse, but it also regulates it. In addition, HCV core protein interacts with toll-like receptors (TLRs) on monocytes, inducing them to produce cytokines. Polyinosinic acid:polycytodylic acid (polyI:C) is a synthetic analogue of double-stranded RNA that binds to TLR3 and can induce secretion of type I IFN from monocytes. Cytokine response against HCV is likely to affect the natural course of infection as well as HCV persistence. However, possible effects of cytokines induced by HCV core protein and polyI:C remain to be investigated. In this study, we isolated CD14(+) monocytes from healthy donors, cultured them in the presence of HCV core protein and/or polyI:C, and characterized the induced cytokines, phenotypes and mechanisms. We demonstrated that HCV core protein- and polyI:C-stimulated CD14(+) monocytes secreted tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-10, and type I interferon (IFN). Importantly, TNF-α and IL-1β regulated the secretion of IL-10, which then influenced the expression of signal transducer and activator of transcription 1 (STAT1) and interferon regulatory factor 1 (IRF1) and subsequently the production of type I IFN. Interestingly, type I IFN also regulated the production of IL-10, which in turn inhibited the nuclear factor (NF)-κB subunit, reducing TNF-α and IL-1β levels. Therefore, IL-10 appears to play a central role in regulating the production of cytokines induced by HCV core protein and polyI:C.

Type I IFN augments IL-27-dependent TRIM25 expression to inhibit HBV replication

Hepatitis B virus (HBV) can cause chronic hepatitis B, which may lead to cirrhosis and liver cancer. Type I interferon (IFN) is an approved drug for the treatment of chronic hepatitis B. However, the fundamental mechanisms of antiviral action by type I IFN and the downstream signaling pathway are unclear. TRIM25 is an IFN-stimulated gene (ISG) that has an important role in RIG-I ubiquitination and activation. Whether TRIM25 is induced in liver cells by type I IFN to mediate anti-HBV function remains unclear. Here we report that interleukin-27 (IL-27) has a critical role in IFN-induced TRIM25 upregulation. TRIM25 induction requires both STAT1 and STAT3. In TRIM25 knockout HepG2 cells, type I IFN production was consistently attenuated and HBV replication was increased, whereas overexpression of TRIM25 in HepG2 cells resulted in elevated IFN production and reduced HBV replication. More interestingly, we found that TRIM25 expression was downregulated in HBV patients and the addition of serum samples from HBV patients could inhibit TRIM25 expression in HepG2 cells, suggesting that HBV might have involved a mechanism to inhibit antiviral ISG expression and induce IFN resistance. Collectively, our results demonstrate that type I IFN -induced TRIM25 is an important factor in inhibiting HBV replication, and the IFN-IL-27-TRIM25 axis may represent a new target for treating HBV infection.

Brucella Dysregulates Monocytes and Inhibits Macrophage Polarization through LC3-Dependent Autophagy

Brucellosis is caused by infection with Brucella species and exhibits diverse clinical manifestations in infected humans. Monocytes and macrophages are not only the first line of defense against Brucella infection but also a main reservoir for Brucella. In the present study, we examined the effects of Brucella infection on human peripheral monocytes and monocyte-derived polarized macrophages. We showed that Brucella infection led to an increase in the proportion of CD14++CD16− monocytes and the expression of the autophagy-related protein LC3B, and the effects of Brucella-induced monocytes are inhibited after 6 weeks of antibiotic treatment. Additionally, the production of IL-1β, IL-6, IL-10, and TNF-α from monocytes in patients with brucellosis was suppressed through the LC3-dependent autophagy pathway during Brucella infection. Moreover, Brucella infection inhibited macrophage polarization. Consistently, the addition of 3-MA, an inhibitor of LC3-related autophagy, partially restored macrophage polarization. Intriguingly, we also found that the upregulation of LC3B expression by rapamycin and heat-killed Brucella in vitro inhibits M2 macrophage polarization, which can be reversed partially by 3-MA. Taken together, these findings reveal that Brucella dysregulates monocyte and macrophage polarization through LC3-dependent autophagy. Thus, targeting this pathway may lead to the development of new therapeutics against Brucellosis.

Type III interferon-induced CBFβ inhibits HBV replication by hijacking HBx

Hepatitis B virus (HBV) and its associated chronic infection remain serious health threats worldwide. However, there is still no impactful approach for clinical treatment of hepatitis B patients. Therefore, developing a better understanding of the interactions between HBV and its host is particularly important. HBV infection has been reported to induce type-III but not type-I or type-II interferon (IFN). In this study, we identified CBFβ, an HIV enhancer, as an HBV restriction factor that is specifically induced by type-III IFN in the early stages of HBV infection. Type-III IFN-induced IL-10 played an important role in the production of CBFβ. Interestingly, the interaction between CBFβ- and HBV-encoded regulatory protein X (HBx) enhanced the stability of CBFβ, but notably blocked HBx-mediated promotion of HBV replication. CBFβ expression was lower in HBV patients than in healthy persons, and the addition of serum from HBV patients inhibited CBFβ expression in HepG2 cells. On the contrary, HBV via HBsAg inhibited type-III IFN-induced CBFβ expression and decreased the anti-HBV activity of type-III IFN, suggesting that HBV inhibits antiviral interferon-stimulated gene (ISG) expression and induces IFN resistance. Collectively, our results demonstrate that type-III IFN-triggered and IL-10-induced CBFβ are crucial factors for inhibiting HBV replication, and the HBx–CBFβ–HBsAg axis reveals a new molecular mechanism of interaction between HBV and its hosts.