Novel strategies to eliminate persistent viral infections

Electro-nape-acupuncture regulates the differentiation of microglia through PD-1/PD-L1 reducing secondary brain injury in acute phase intracerebral hemorrhage rats

INTRODUCTION

This study aimed to investigate the effect of electro-nape-acupuncture (ENA) on the differentiation of microglia and the secondary brain injury in rats with acute-phase intracerebral hemorrhage (ICH) through the programmed cell death protein-1/ligand-1 (PD-1/PD-L1) pathway.

METHODS

A total of 27 male Sprague-Dawley rats were randomly divided into three groups: sham group, ICH group, and ENA group. The autologous blood infusion intracerebral hemorrhage model was used to study the effects of ENA by administering electroacupuncture at GB20 (Fengchi) and Jiaji (EX-B2) acupoints on 24 h after the modeling, once per day for 3 days. The neurological function damage, hematoma lesion, and inflammatory cell infiltration were measured by the beam walking test and hematoxylin-eosin staining. The expression of PD-1, PD-L1, CD86, CD206, and related cytokines around the hematoma was measured by western blot, quantitative reverse transcription polymerase chain reaction, and immunofluorescence.

RESULTS

The ICH group had significant neurological deficits (p < .001), hematoma lesions, and inflammatory cell infiltration. The levels of CD86 protein, inflammatory factors tumor necrosis factors (TNF)-α, interleukin (IL)-1β, and IL-6 were increased (p < .001), while CD206 protein was reduced (p < .01), and the number of CD86+ /CD11b+ cells was also increased (p < .001) compared to the sham group. However, after ENA intervention, there was a significant reduction in neurological function damage (p < .05), infiltration of inflammatory cells, and the expression levels of CD86+ /CD11b+ cells (p < .05), resulting in the increased expression of PD-1 protein and differentiation of M2 phenotype significantly (p < .001).

CONCLUSION

The study concludes that ENA could reduce neurological function damage, inhibit the expression of pro-inflammatory cytokines, and improve the infiltration of inflammatory cells to improve secondary brain injury in acute-phase intracerebral hemorrhage rats. These effects could be related to the increased expression of PD-1 around the lesion, promoting the differentiation of microglia from M1 to M2 phenotype.

Canine Distemper Virus Alters Defense Responses in an Ex Vivo Model of Pulmonary Infection

Canine distemper virus (CDV), belonging to the genus Morbillivirus, is a highly contagious pathogen. It is infectious in a wide range of host species, including domestic and wildlife carnivores, and causes severe systemic disease with involvement of the respiratory tract. In the present study, canine precision-cut lung slices (PCLSs) were infected with CDV (strain R252) to investigate temporospatial viral loads, cell tropism, ciliary activity, and local immune responses during early infection ex vivo. Progressive viral replication was observed during the infection period in histiocytic and, to a lesser extent, epithelial cells. CDV-infected cells were predominantly located within the bronchial subepithelial tissue. Ciliary activity was reduced in CDV-infected PCLSs, while viability remained unchanged when compared to controls. MHC-II expression was increased in the bronchial epithelium on day three postinfection. Elevated levels of anti-inflammatory cytokines (interleukin-10 and transforming growth factor-β) were observed in CDV-infected PCLSs on day one postinfection. In conclusion, the present study demonstrates that PCLSs are permissive for CDV. The model reveals an impaired ciliary function and an anti-inflammatory cytokine response, potentially fostering viral replication in the lung during the early phase of canine distemper.

Umifenovir Epigenetically Targets the IL-10 Pathway in Therapy against Coxsackievirus B4 Infection

Umifenovir, a broad-spectrum nonnucleoside antiviral drug, has a promising efficacy against coxsackievirus B4 (CVB4) infection, but its mechanism remains unclear. CVB4 is a common human single-stranded RNA virus that belongs to the Picornaviridae family and the Enterovirus genus. Enterovirus can cause severe diseases, such as meningitis, myocarditis, pancreatitis, insulin-dependent diabetes, and several other diseases, in both adults and children. We have previously demonstrated the critical role of interleukin 10 (IL-10) in promoting CVB4 infection and the downregulation of IL-10 by umifenovir. To further explore the underlying mechanisms of umifenovir, we characterized the epigenetic regulation of IL-10 in IL-10 knockout RAW264.7 cells and a BALB/c mouse splenocyte model. Mechanistically, we found that umifenovir inhibited CVB4-activated IL-10 by enhancing the methylation level of the repressive histones H3K9me3 and H3K27me3 while reducing the acetylation level of the activating histone H3K9ac in the promoter region of the IL-10 gene. Furthermore, using a chromosome conformation capture approach, we discovered that CVB4 infection activated the IL-10 gene by forming an intrachromosomal interaction between the IL-10 gene promoter and an intronic enhancer of the downstream MK2 (mitogen-activated protein kinase [MAPK]-activated protein kinase 2 [MAPKAPK2]) gene, a critical component of the p38-MAPK signaling pathway, which is required for IL-10 gene expression. However, umifenovir treatment abolished this spatial conformation and chromatin interaction, thus reducing the continuous expression of IL-10 and subsequent CVB4 replication. In conclusion, this study reveals a novel epigenetic mechanism by which umifenovir controls CVB4 infections, thus laying a theoretical foundation for therapeutic use of umifenovir. IMPORTANCE Viral infections are major threats to human health because of their strong association with a variety of inflammation-related diseases, especially cancer. Many antiviral drugs are performing poorly in treating viral infections. This is probably due to the immunosuppressive effect of highly expressed IL-10, which is caused by viral infection. Umifenovir is a broad-spectrum antiviral drug. Our recent studies showed that umifenovir has a significant inhibitory effect on CVB4 infection and can reduce IL-10 expression caused by CVB4. However, another antiviral drug, rupintrivir, showed good antiviral activity but had no effect on the expression of IL-10. This suggests that the regulation of IL-10 expression is a key part of the antiviral mechanism of umifenovir. Therefore, due to the dual function of the inhibition of CVB4 replication and the regulation of immune antiviral pathway, the mechanism of umifenovir is of great value to study.

IL-10 Promoter -592 Polymorphism may Influence Susceptibility to HIV Infection in South Indian Population

BACKGROUND

Genetic factors play an important role in the development of disease susceptibility or protection. Cytokine gene polymorphisms are reported to be associated with altered levels of cytokine production that can impact disease progression in HIV and TB.

OBJECTIVE

In this study, we studied IL-10 -592(C/A) and TGF-β -509 (C/T) promoter polymorphisms to understand their role in susceptibility or resistance to HIV and TB in a South Indian population.

METHOD

Genomic DNA was isolated from healthy controls, pulmonary tuberculosis patients (n=122) and HIV positive individuals (n=100) and used for genotyping by polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

Results revealed that under dominant model (CC vs CA+AA), IL-10 -592 'A' allele either 'CA' or 'AA' combinations significantly associated with susceptibility to HIV compared to healthy controls (OR: 1.88(1.05-3.35); p=0.030). However, we found no significant association with TB. TGF-β -509 polymorphism did not associate with either HIV or TB under overdominant model. Neither of the promoter polymorphisms associated with sex in either HIV or TB. However, a trend towards higher risk to HIV was found in females compared with males in IL-10 -592 'AA' genotype.

CONCLUSION

This study suggests the association of IL-10 -592 "AA" genotype with susceptibility to HIV under dominant model in the Southern Indian population. Future studies are needed with a larger sample size in order to confirm the observations made in this study.

Increased PD-1 Expression and Altered T Cell Repertoire Diversity Predict Mortality in Patients with Septic Shock: A Preliminary Study

Sepsis causes impairment of innate and adaptive immunity by multiple mechanisms, including depletion of immune effector cells and T cell exhaustion. Although lymphocyte dysfunction is associated with increased mortality and potential reactivation of latent viral infection in patients with septic shock, the relation between viral reactivation and lymphocyte dysfunction is obscure. The objectives of this study were 1) to determine the relation of lymphocyte dysfunction to viral reactivation and mortality, and 2) to evaluate recovery of lymphocyte function during septic shock, including T cell receptor (TCR) diversity and the expression of programmed death 1 (PD-1). In 18 patients with septic shock and latent cytomegalovirus (CMV) infection, serial blood samples were obtained on days 1, 3, and 7 after the onset of shock, and immune cell subsets and receptor expression were characterized by flow cytometry. TCR diversity of peripheral blood mononuclear cells was analyzed by Multi-N-plex PCR, and CMV DNA was quantified using a real-time PCR kit. A decrease of TCR diversity and monocyte HLA-DR expression were observed in the early stage of septic shock, while CD4+ T cells displayed an increase of PD-1 expression. Significant lymphopenia persisted for at least 7 days following the onset of septic shock. Normalization of TCR diversity and PD-1 expression was observed by day 7, except in patients who died. CMV reactivation was detected in 3 of the 18 patients during the first week of their ICU stay and all 3 patients died. These changes are consistent with the early stage of immune cell exhaustion and indicate the importance of normal lymphocyte function for recovery from septic shock. Ongoing lymphocyte dysfunction is associated with CMV reactivation and dissemination, as well as with unfavorable outcomes.

Bovine Viral Diarrhea Virus Infects Monocyte-Derived Bovine Dendritic Cells by an E2-Glycoprotein-Mediated Mechanism and Transiently Impairs Antigen Presentation

Infection of professional antigen presenting cells by viruses can have a marked effect on these cells and important consequences for the generation of subsequent immune responses. In this study, we demonstrate that different strains of bovine viral diarrhea virus (BVDV) infect bovine dendritic cells differentiated from nonadherent peripheral monocytes (moDCs). BVDV did not cause apoptosis in these cells. Infection of moDC was prevented by incubating the virus with anti-E2 antibodies or by pretreating the cells with recombinant E2 protein before BVDV contact, suggesting that BVDV infects moDC through an E2-mediated mechanism. Virus entry was not reduced by incubating moDC with Mannan or ethylenediaminetetraacetic acid (EDTA) before infection, suggesting that Ca(2+) and mannose receptor-dependent pathways are not mediating BVDV entry to moDC. Infected moDC did not completely upregulate maturation surface markers. Infection, but not treatment with inactivated virus, prevented moDC to present a third-party antigen to primed CD4(+) T cells within the first 24 hours postinfection (hpi). Antigen-presenting capacity was recovered when viral replication diminished at 48 hpi, suggesting that active infection may interfere with moDC maturation. Altogether, our results suggest an important role of infected DCs in BVDV-induced immunopathogenesis.

Canine distemper virus infection leads to an inhibitory phenotype of monocyte-derived dendritic cells in vitro with reduced expression of co-stimulatory molecules and increased interleukin-10 transcription

Canine distemper virus (CDV) exhibits a profound lymphotropism that causes immunosuppression and increased susceptibility of affected dogs to opportunistic infections. Similar to human measles virus, CDV is supposed to inhibit terminal differentiation of dendritic cells (DCs), responsible for disturbed repopulation of lymphoid tissues and diminished antigen presenting function in dogs. In order to testify the hypothesis that CDV-infection leads to an impairment of professional antigen presenting cells, canine DCs have been generated from peripheral blood monocytes in vitro and infected with CDV. Virus infection was confirmed and quantified by transmission electron microscopy, CDV-specific immunofluorescence, and virus titration. Flow cytometric analyses revealed a significant down-regulation of the major histocompatibility complex class II and co-stimulatory molecules CD80 and CD86 in CDV-infected DCs, indicative of disturbed antigen presenting capacity. Molecular analyses revealed an increased expression of the immune inhibitory cytokine interleukin-10 in DCs following infection. Results of the present study demonstrate that CDV causes phenotypical changes and altered cytokine expression of DCs, which represent potential mechanisms to evade host immune responses and might contribute to immune dysfunction and virus persistence in canine distemper.

Blockade of the negative co-stimulatory molecules PD-1 and CTLA-4 improves survival in primary and secondary fungal sepsis

Introduction

Fungal sepsis is an increasingly common problem in intensive care unit patients.Mortality from fungal sepsis remains high despite antimicrobial therapy that is highly active against most fungal pathogens, a finding consistent with defective host immunity that is present in many patients with disseminated fungemia.One recently recognized immunologic defect that occurs in patients with sepsis is T cell "exhaustion" due to increased expression of programmed cell death -1 (PD-1).This study tested the ability of anti-PD-1 and anti-programmed cell death ligand -1 (anti-PD-L1) antagonistic antibodies to improve survival and reverse sepsis-induced immunosuppression in two mouse models of fungal sepsis.

Methods

Fungal sepsis was induced in mice using two different models of infection, that is, primary fungal sepsis and secondary fungal sepsis occurring after sub-lethal cecal ligation and puncture (CLP).Anti-PD-1 and anti-PD-L1 were administered 24 to 48 h after fungal infection and effects on survival, interferon gamma production, and MHC II expression were examined.

Results

Anti-PD-1 and anti-PD-L1 antibodies were highly effective at improving survival in primary and secondary fungal sepsis.Both antibodies reversed sepsis-induced suppression of interferon gamma and increased expression of MHC II on antigen presenting cells.Blockade of cytotoxic T-lymphocyte antigen-4 (CTLA-4), a second negative co-stimulatory molecule that is up-regulated in sepsis and acts like PD-1 to suppress T cell function, also improved survival in fungal sepsis.

Conclusions

Immuno-adjuvant therapy with anti-PD-1, anti-PD-L1 and anti-CTLA-4 antibodies reverse sepsis-induced immunosuppression and improve survival in fungal sepsis.The present results are consistent with previous studies showing that blockade of PD-1 and CTLA-4 improves survival in bacterial sepsis.Thus, immuno-adjuvant therapy represents a novel approach to sepsis and may have broad applicability in the disorder.Given the relative safety of anti-PD-1 antibody in cancer clinical trials to date, therapy with anti-PD-1 in patients with life-threatening sepsis who have demonstrable immunosuppression should be strongly considered.

The role of pro- and anti-inflammatory cytokines in the pathogenesis of spontaneous canine CNS diseases

Dogs are comparatively frequently affected by various spontaneously occurring inflammatory and degenerative central nervous system (CNS) conditions, and immunopathological processes are a hallmark of the associated neuropathology. Due to the low regenerative capacity of the CNS a sophisticated understanding of the underlying molecular basis for disease initiation, progression and remission in canine CNS diseases represents a prerequisite for the development of novel therapeutical approaches. In addition, as many spontaneous canine CNS diseases share striking similarities with their human counterpart, knowledge about the immune pathogenesis may in part be translated for a better understanding of certain human diseases. In addition to cytokine-driven differentiation of peripheral leukocytes including different subsets of T cells recent research suggests a pivotal role of these mediators also in phenotype polarization of resident glial cells. Cytokines thus represent the key mediators of the local and systemic immune response in CNS diseases and their orchestration significantly decides on either lesion progression or remission. The aim of the present review is to summarize the growing number of data focusing on the molecular basis of the immune response during spontaneous canine CNS diseases and to detail the effect of cytokines on the immune pathogenesis of selected idiopathic, infectious, and traumatic canine CNS diseases. Steroid-responsive meningitis arteritis (SRMA) represents a unique idiopathic disease of leptomeningeal blood vessels characterized by excessive IgA secretion into the cerebrospinal fluid. Recent reports have given sophisticated insights into the cytokine-driven, immune-mediated pathogenesis of SRMA that is characterized by a biased T helper 2 cell response. Canine distemper associated leukoencephalitis represents an important spontaneously occurring disease that allows investigations on the basic pathogenesis of immune-mediated myelin loss. It is characterized by an early virus-induced up-regulation of pro-inflammatory cytokines with chronic bystander immune-mediated demyelinating processes. Lastly, canine spinal cord injury (SCI) shares many similarities with the human counterpart and most commonly results from intervertebral disk disease. The knowledge of its pathogenesis is largely restricted to experimental studies in rodents, and the impact of immune processes that accompany secondary injury is discussed controversially. Recent investigations on canine SCI highlight the pivotal role of pro-inflammatory cytokine expression that is paralleled by a dominating reaction of microglia/macrophages potentially indicating a polarization of these immune cells into a neurotoxic and harmful phenotype. This report will review the role of cytokines in the immune processes of the mentioned representative canine CNS diseases and highlight the importance of cytokine/cytokine interaction as a useful therapeutic target in canine CNS diseases.

IPNV modulation of pro and anti-inflammatory cytokine expression in Atlantic salmon might help the establishment of infection and persistence

IPNV is the agent of a well-characterized acute disease that produces a systemic infection and high mortality in farmed fish species and persistent infection in surviving fish after outbreaks. Because modulation of the host expression of pro and anti-inflammatory cytokines can help establish persistence, in this study, we examined the expression of IL-1β, IL-8, IFNα1 and IL-10 during acute and persistent IPNV infection of Atlantic salmon. Results showed that IPNV infection induces an increase of the IFNα1 and IL-10 mRNA levels in the spleen and head kidney (HK) of fish after acute experimental infection. Levels of the pro-inflammatory cytokines IL-1β and IL-8 did not rise in the spleen although an increase of IL-1β, but not of IL-8, was observed in head kidney. In carrier asymptomatic salmon, cytokine gene expression of IFNα1 in the spleen and IL-10 in head kidney were also significantly higher than expression in non-carrier fish. Interestingly, a decrease of IL-8 expression was also observed. IPNV infection of SHK-1, which is a macrophage-like cell line of salmon, also induced an increase of expression of the anti-inflammatory cytokine IL-10 with no effects on the expression of IL-1β and IL-8. The effects are induced by an unknown mechanism during viral infection because poly I:C and the viral genomic dsRNA showed the opposite effects on cytokine expression in SHK-1 cells. In summary, IPNV always induces up-regulation of the anti-inflammatory cytokine IL-10 in Atlantic salmon. As this is accompanied by a lack of induction of the pro-inflammatory cytokines IL-1β and IL-8, the anti-inflammatory milieu may explain the high frequency, prevalence and persistence of IPNV in salmon. Effects might be part of the viral mechanisms of immune evasion.

Association of IL-10-promoter genetic variants with the rate of CD4 T-cell loss, IL-10 plasma levels, and breadth of cytotoxic T-cell lymphocyte response during chronic HIV-1 infection

BACKGROUND

Interleukin-10 (IL-10) is a potent immunoregulatory cytokine. IL-10-promoter polymorphisms have been shown to affect human immunodeficiency virus type 1 (HIV-1) clinical outcomes but the underlying mechanisms are poorly understood.

METHODS

We investigated the relationship between IL-10-promoter variants, plasma cytokine levels, immune responses and markers of disease outcome in antiretroviral-naïve HIV-1 chronically infected individuals from South Africa. Two IL-10-promoter single nucleotide polymorphisms (SNPs) were genotyped in 451 participants. Baseline plasma levels of select cytokines were measured for 112 individuals. Viral load, CD4(+) T-cell counts and HIV-1-specific interferon-gamma CD8(+) T-cell immune responses were measured at baseline. CD4(+) T-cell counts were measured longitudinally and rates of CD4(+) T-cell decline computed for 300 study subjects.

RESULTS

The minor IL-10-1082G and -592A variants occurred at frequencies of 0.31 and 0.34, respectively. The -592AA genotype associated significantly with attenuated loss of CD4(+) T cells (P = .0496). Individuals possessing -1082GG had significantly higher IL-10 levels compared to -1082AA/AG (P = .0006). The -592AA genotype was associated with greater breadth of virus-specific CD8(+) T-cell responses compared to CC and CA (P = .002 and .004 respectively).

CONCLUSIONS

IL-10-promoter variants may influence the rate of HIV-1 disease progression by regulating IL-10 levels and the breadth of CD8(+) T-cell immune responses.

Phagocytosis, a potential mechanism for myeloid-derived suppressor cell regulation of CD8+ T cell function mediated through programmed cell death-1 and programmed cell death-1 ligand interaction

CD8(+) T cells become exhausted, inducing cell surface protein programmed cell death-1 (PD-1) as chronic virus diseases or tumors progress, but underlying mechanisms of this are unclear. We previously showed that M-CSF is important for developing tolerogenic dendritic cells (DCs) from human CD14(+) monocytes. In this article, we identify M-CSF-derived DCs (M-DCs) after stimulation with IL-10 as myeloid-derived suppressor cells with additional tolerogenic activities to CD8(+) T cells. IL-10 increased PD-1 ligand expression on M-DC, and IL-10-stimulated M-DCs (M-DC/IL-10) induced expression of PD-1 on, and apoptosis of, CD8(+) T cells and phagocytosed CD8(+) T cells. Enhanced phagocytic activity of M-DC/IL-10 required IFN-γ, which further increased PD-1 ligand and PD-2 ligand expression on M-DC/IL-10. IFN-γ-stimulated M-DC/IL-10 cells were phenotypically macrophage-like cells with little or no expression of CD86, a costimulatory molecule, but with high expression levels of CD14, CD200R, and CD80. No phagocytic activity was detected with GM-CSF-derived DCs. We propose that phagocytosis by IFN-γ-stimulated M-DC/IL-10 cells, which may be DCs or, alternatively, a unique subset of macrophages, may be a mechanism by which IFN-γ-producing CD8(+) T cells are tolerized after type 1 immune responses to chronic virus or tumor, and that IFN-γ links effector CD8(+) T cells to their phagocytic clearance.

Programmed death (PD)-1-deficient mice are extremely sensitive to murine hepatitis virus strain-3 (MHV-3) infection

The inhibitory receptor programmed death-1 (PD-1) has the capacity to maintain peripheral tolerance and limit immunopathological damage; however, its precise role in fulminant viral hepatitis (FH) has yet to be described. Here, we investigated the functional mechanisms of PD-1 as related to FH pathogenesis induced by the murine hepatitis virus strain-3 (MHV-3). High levels of PD-1-positive CD4⁺, CD8⁺ T cells, NK cells and macrophages were observed in liver, spleen, lymph node and thymus tissues following MHV-3 infection. PD-1-deficient mice exhibited significantly higher expression of the effector molecule which initiates fibrinogen deposition, fibrinogen-like protein 2 (FGL2), than did their wild-type (WT) littermates. As a result, more severe tissue damage was produced and mortality rates were higher. Fluorescence double-staining revealed that FGL2 and PD-1 were not co-expressed on the same cells, while quantitative RT-PCR demonstrated that higher levels of IFN-γ and TNF-α mRNA transcription occurred in PD-1-deficient mice in response to MHV-3 infection. Conversely, in vivo blockade of IFN-γ and TNF-α led to efficient inhibition of FGL2 expression, greatly attenuated the development of tissue lesions, and ultimately reduced mortality. Thus, the up-regulation of FGL2 in PD-1-deficient mice was determined to be mediated by IFN-γ and TNF-α. Taken together, our results suggest that PD-1 signaling plays an essential role in decreasing the immunopathological damage induced by MHV-3 and that manipulation of this signal might be a useful strategy for FH immunotherapy.

The principal characteristic of fulminant viral hepatitis (FH) induced by the murine hepatitis virus strain-3 (MHV-3) is severe hepatocellular necrosis, which is mediated by the fibrinogen-like protein 2 (FGL2), a molecule that has the capacity to promote fibrinogen deposition and activate the coagulation cascades. Here, we report that MHV-3 infection of program death-1 (PD-1)-deficient mice results in tissue damage throughout multiple organs, including the liver, spleen, thymus and lymph nodes. The liver damage, in particular, occurred earlier and was more severe in PD-1-deficient mice than in their wild type (WT) littermates. Further investigation determined that MHV-3 infection was associated with high levels of IFN-γ and TNF-α in the damaged organs of PD-1-deficient mice. Conversely, intraperitoneal injection of a combination of anti-IFN-γ and anti-TNF-α blocking mAbs led to inhibition of FGL2 expression, greatly attenuated tissue lesions and reduced mortality. Our results demonstrate that PD-1 signaling controls immunopathological damage following MHV-3 infection, indicating that manipulation of the PD-1 signal might represent a useful strategy for FH immunotherapy.

Involvement of the PD-1/PD-L pathway in outcome of hepatitis B virus infection

Programmed death 1 (PD-1) is a costimulatory molecule which can be expressed on T cells. PD-1 and its ligands (PD-Ls) have been demonstrated to be able to inhibit the effector functions of T cells and even result in T cell function. Recently, many studies have demonstrated that the activation of the PD-1/PD-L pathway may affect the outcome of HBV infection. Blockade of the PD-1/PD-L pathway may enhance body's immune responses, which provides a new avenue for therapy of chronic hepatitis B.

Antibodies to human IL-10 neutralize ebvIL-10-mediated cytokine suppression but have no effect on cmvIL-10 activity

Interleukin-10 is a pivotal determinant of virus clearance or persistence. Two human herpesviruses, Epstein-Barr virus (EBV) and human cytomegalovirus (HCMV) are unique among persistent viruses because they not only trigger production of host IL-10, but both viruses also encode homologs of IL-10 that are expressed during infection. Because anti-human IL-10 antibodies have diagnostic value and therapeutic potential for many chronic infections, cross-reactivity with ebvIL-10 and cmvIL-10 was evaluated in this study. Six of seven anti-hIL-10 antibodies tested recognized ebvIL-10 and neutralized its immunosuppressive activity. In contrast, cmvIL-10 was neither recognized nor neutralized by any anti-human IL-10 antibody. These findings demonstrate that IL-10-neutralizing treatments in HCMV- or EBV-infected patients may require consideration of the contribution of viral IL-10 to disease pathology.

IL-10 induces aberrant deletion of dendritic cells by natural killer cells in the context of HIV infection

Persistent levels of IL-10 play a central role in progressive immune dysfunction associated with chronic viral infections such as HIV, but the underlying mechanisms are poorly understood. Because IL-10 affects the phenotypic and functional properties of DCs, which are responsible for initiating adaptive immune responses, we investigated whether IL-10 induces changes in DC phenotype and function in the context of HIV infection. Here, we show that IL-10 treatment of immature and mature human DCs in culture induced contrasting phenotypic changes in these populations: immature DCs exhibited aberrant resistance to NK cell-mediated elimination, whereas mature DCs exhibited increased susceptibility to NKG2D-dependent NK elimination. Treatment of immature and mature DCs with HIV resulted in potent IL-10 secretion and the same phenotypic and functional changes observed in the IL-10-treated cells. Consistent with these in vitro data, LNs isolated from individuals infected with HIV exhibited aberrant accumulation of a partially "immature" DC population. Together, these data suggest that the progressive immune dysfunction observed in chronic viral infections might be caused in part by IL-10-induced reversal of DC susceptibility to NK cell-mediated elimination, resulting in the accumulation of poorly immunogenic DCs in LNs, the sites of adaptive immune response induction.

Persistent chronic inflammation and infection by Chikungunya arthritogenic alphavirus in spite of a robust host immune response

Alphaviruses, including Chikungunya virus (CHIKV), produce a transient illness in humans, but severe forms leading to chronic incapacitating arthralgia/arthritis have been reported by mechanisms largely ill-characterized. The pathogenesis of CHIKV was addressed in a prospective cohort study of 49 hospitalized patients from Reunion Island subsequently categorized into two distinct groups at 12 mo postinfection. Comprehensive analyses of the clinical and immunological parameters throughout the disease course were analyzed in either the "recovered" or the "chronic" groups to identify prognostic markers of arthritis-like pathology after CHIKV disease. We found that the chronic group consisted mainly of more elderly patients (>60 y) and with much higher viral loads (up to 10(10) viruses per milliliter of blood) during the acute phase. Remarkably, a rapid innate immune antiviral response was demonstrated by robust dendritic/NK/CD4/CD8 cell activation and accompanied by a rather weak Th1/Th2 cytokine response in both groups. Interestingly, the antiviral immune response witnessed by high levels of IFN-alpha mRNA in PBMCs and circulating IL-12 persisted for months only in the chronic group. CHIKV (RNA and proteins) was found in perivascular synovial macrophages in one chronic patient 18 mo postinfection surrounded by infiltrating NK and T cells (CD4(++) but rare cytotoxic CD8). Fibroblast hyperplasia, strong angiogenesis, tissue lesions given the high levels of matrix metalloproteinase 2, and acute cell death [high cleaved poly(ADP-ribose) polymerase staining] were observed in the injured synovial tissue. These observed cellular and molecular events may contribute to chronic arthralgia/arthritis targeted by methotrexate used empirically for effective treatment but with immunosuppressive function in a context of viral persistence.

Lessons learned from natural infection: focusing on the design of protective T cell vaccines for HIV/AIDS

CD8(+) cytotoxic T lymphocyte (CTL) responses are crucial in establishing the control of persistent virus infections. Population studies of HIV-1-infected individuals suggest that CD8(+) CTL responses targeting epitopes that take the greatest toll on virus replication are instrumental in immune control. A major question for vaccine design is whether incorporating epitopes responsible for controlling a persistent virus will translate into protection from natural infection or serve solely as a fail-safe mechanism to prevent overt disease in infected individuals. Here, we discuss qualitative parameters of the CD8(+) CTL response and mechanisms operative in the control of persistent virus infections and suggest new strategies for design and delivery of HIV vaccines.

Negative immune regulator Tim-3 is overexpressed on T cells in hepatitis C virus infection and its blockade rescues dysfunctional CD4+ and CD8+ T cells

A number of emerging molecules and pathways have been implicated in mediating the T-cell exhaustion characteristic of chronic viral infection. Not all dysfunctional T cells express PD-1, nor are they all rescued by blockade of the PD-1/PD-1 ligand pathway. In this study, we characterize the expression of T-cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) in chronic hepatitis C infection. For the first time, we found that Tim-3 expression is increased on CD4(+) and CD8(+) T cells in chronic hepatitis C virus (HCV) infection. The proportion of dually PD-1/Tim-3-expressing cells is greatest in liver-resident T cells, significantly more so in HCV-specific than in cytomegalovirus-specific cytotoxic T lymphocytes. Tim-3 expression correlates with a dysfunctional and senescent phenotype (CD127(low) CD57(high)), a central rather than effector memory profile (CD45RA(negative) CCR7(high)), and reduced Th1/Tc1 cytokine production. We also demonstrate the ability to enhance T-cell proliferation and gamma interferon production in response to HCV-specific antigens by blocking the Tim-3-Tim-3 ligand interaction. These findings have implications for the development of novel immunotherapeutic approaches to this common viral infection.

PD-1 signaling in primary T cells

SUMMARY

Programmed death-1 (PD-1) is a cell surface molecule that regulates the adaptive immune response. Engagement of PD-1 by its ligands PD-L1 or PD-L2 transduces a signal that inhibits T-cell proliferation, cytokine production, and cytolytic function. While a great deal is known concerning the biologic roles PD-1 plays in regulating the primary immune response and in T-cell exhaustion, comparatively little is known regarding how PD-1 ligation alters signaling pathways. PD-1 ligation is known to inhibit membrane-proximal T-cell signaling events, while ligation of the related inhibitory molecule cytotoxic T-lymphocyte antigen-4 appears to target more downstream signaling pathways. A major obstacle to an in-depth understanding of PD-1 signaling is the lack of physiologic models in which to study signal transduction. This review focuses on: (i) signaling pathways altered by PD-1 ligation, (ii) factors recruited upon PD-1 phosphorylation, and (iii) exploring the hypothesis that PD-1 ligation induces distinct signals during various stages of immune-cell differentiation. Lastly, we describe models to dissect the function of the PD-1 cytoplasmic tail using primary cells in the absence of agonist antibodies.

NKT cell immune responses to viral infection

BACKGROUND

Natural killer T (NKT) cells are a heterogeneous population of innate T cells that have attracted interest because of their potential to regulate immune responses to a variety of pathogens. The most widely studied NKT cell subset is the invariant (i)NKT cells that recognize glycolipids in the context of the CD1d molecule. The multifaceted methods of activation iNKT cells possess and their ability to produce regulatory cytokines has made them a primary target for studies.

OBJECTIVE/METHODS

To give insights into the roles of iNKT cells during infectious diseases, particularly viral infections. We also highlight mechanisms leading to iNKT cell activation in response to pathogens.

CONCLUSIONS

iNKT cell's versatility allows them to detect and respond to several viruses. Therapeutic approaches to specifically target iNKT cells will require additional research. Notably, the roles of non-invariant NKT cells in response to pathogens warrant further investigation.

Ligation of TLR9 induced on human IL-10-secreting Tregs by 1alpha,25-dihydroxyvitamin D3 abrogates regulatory function

Signaling through the TLR family of molecular pattern recognition receptors has been implicated in the induction of innate and adaptive immune responses. A role for TLR signaling in the maintenance and/or regulation of Treg function has been proposed, however its functional relevance remains unclear. Here we have shown that TLR9 is highly expressed by human Treg secreting the antiinflammatory cytokine IL-10 induced following stimulation of blood and tissue CD3+ T cells in the presence of 1alpha,25-dihydroxyvitamin D3 (1alpha25VitD3), the active form of Vitamin D, with or without the glucocorticoid dexamethasone. By contrast, TLR9 was not highly expressed by naturally occurring CD4+CD25+ Treg or by Th1 and Th2 effector cells. Induction of TLR9, but not other TLRs, was IL-10 dependent and primarily regulated by 1alpha25VitD3 in vitro. Furthermore, ingestion of calcitriol (1alpha25VitD3) by human volunteers led to an increase of both IL-10 and TLR9 expression by CD3+CD4+ T cells analyzed directly ex vivo. Stimulation of 1alpha25VitD3-induced IL-10-secreting Treg with TLR9 agonists, CpG oligonucleotides, resulted in decreased IL-10 and IFN-gamma synthesis and a concurrent loss of regulatory function, but, unexpectedly, increased IL-4 synthesis. We therefore suggest that TLR9 could be used to monitor and potentially modulate the function of 1alpha25VitD3-induced IL-10-secreting Treg in vivo, and that this has implications in cancer therapy and vaccine design.

The race between infection and immunity: how do pathogens set the pace?

Infection is often referred to as a race between pathogen and immune response. This metaphor suggests that slower growing pathogens should be more easily controlled. However, a growing body of evidence shows that many chronic infections are caused by failure to control slow growing pathogens. The slow growth of pathogens seems to directly affect the kinetics of the immune response. Compared with the response to fast growing pathogens, the T-cell response to slow pathogens is delayed in its initiation, lymphocyte expansion is slow and the response often fails to clear the pathogen, leading to chronic infection. Understanding the 'rules of the race' for slow growing pathogens has important implications for vaccine design and immune control of many chronic infections.

Virus-specific host miRNAs: antiviral defenses or promoters of persistent infection?

The discovery of host-microRNA (miRNA) targets in the genomes of many vertebrate viruses indicates that the corresponding miRNAs are a part of the host's innate antiviral defense. However, given that viruses evolve much faster than host miRNAs, it is surprising that viral variants lacking these 'antiviral' miRNA target sequences have not become established. We present an alternate view that miRNAs are among the host molecules that viruses co-opt to suppress their own replication to evade immune elimination and establish a persistent infection. The presence of host-miRNA targets in the genomes of rapidly evolving viruses probably reflects the adaptation of these viruses to the cellular miRNA milieu.

Programmed death 1 expression during antiviral treatment of chronic hepatitis B: Impact of hepatitis B e-antigen seroconversion

Hyperexpression of the programmed death 1 (PD-1) molecule is a hallmark of exhausted T-cells, having a negative impact on T-cell activation and function. We studied longitudinally 18 hepatitis B e antigen (HBeAg)-positive patients undergoing treatment with direct antivirals (telbivudine or lamivudine) to determine the relationship between treatment-induced viremia reduction and HBeAg seroconversion with respect to PD-1 levels and T-cell reactivity. PD-1 expression was assessed by (1) flow cytometry and (2) quantitative real-time polymerase chain reaction; hepatitis B virus (HBV)-specific CD8+ T-cells were quantitated by pentamer staining; T-cell reactivity to HBV antigens was determined by interferon gamma (IFNgamma) and interleukin 10 (IL-10) enzyme-linked immunosorbent spot (ELISPOT) assays; and central/effector memory phenotypes were defined by phenotypic markers. PD-1 expression correlated closely with viremia levels. On therapy, PD-1 decreased significantly on total CD8+ T-cells, HBV-specific CD8+ T-cells, and CD3+/CD8- T-cells both as the percentage of positive cells (P < 0.01) and as the mean fluorescent intensity (P < 0.05), and this was paralleled by a marked reduction of PD-1 messenger RNA levels (P = 0.001). HBeAg serocoversion (in 6/18 patients) resulted in a further PD-1 decrease with a 50% reduction in the frequency of PD-1+/CD8+ T-cells, which was not observed in patients remaining HBeAg-positive. The decrease in PD-1 expression was associated with increased frequencies of IFNgamma-producing T-cells and decreased frequencies of IL-10 producing T-cells. At baseline, PD-1 expression correlated directly with the frequency of hepatitis B core antigen (HBcAg) central and effector memory phenotypes, whereas an inverse correlation was observed between PD-1 expression and HBcAg-specific effector phenotypes.

CONCLUSION

These results demonstrate that in chronic HBV infection, both viremia levels and HBeAg drive PD-1 expression and resulting T-cell impairment. Treatment-induced suppression of HBV replication reduces PD-1 expression; however, additional immunotherapeutic interventions are needed for restoration of T-cell functions.