Cytokine homologs of human gammaherpesviruses

Molecular mimicry in the pathogenesis of autoimmune rheumatic diseases

Autoimmune rheumatic diseases (ARDs) are a heterogeneous group of conditions characterized by excessive and misdirected immune responses against the body's own musculoskeletal tissues. Their exact aetiology remains unclear, with genetic, demographic, behavioural and environmental factors implicated in disease onset. One prominent hypothesis for the initial breach of immune tolerance (leading to autoimmunity) is molecular mimicry, which describes structural or sequence similarities between human and microbial proteins (mimotopes). This similarity can lead to cross-reactive antibodies and T-cell receptors, resulting in an immune response against autoantigens. Both commensal microbes in the human microbiome and pathogens can trigger molecular mimicry, thereby potentially contributing to the onset of ARDs. In this review, we focus on the role of molecular mimicry in the onset of rheumatoid arthritis and systemic lupus erythematosus. Moreover, implications of molecular mimicry are also briefly discussed for ankylosing spondylitis, systemic sclerosis and myositis.

Cytokine Dynamics and Herpesvirus Interactions in Pediatric Liver and Kidney Transplant Recipients: The Distinct Behavior of HCMV, HHV6, HHV7 and EBV

Pediatric solid organ transplant (SOT) recipients face a challenging balance between immunosuppression and graft rejection. While Epstein-Barr Virus (EBV) and cytomegalovirus (HCMV) are known contributors to post-transplant lymphoproliferative disease and graft rejection, respectively, the roles of herpesvirus 6 and 7 (HHV6 and HHV7) and the impact of these herpesviruses on cytokine levels remain unclear, leading to gaps in clinical practice. In this associative study, we measured 17 cytokines using a Bio-Plex assay in a meticulously curated plasma sample pool (N = 158) from pediatric kidney and liver transplant recipients over a one-year follow-up period. The samples included virus-negative and virus-positive cases, either individually or in combination, along with episodes of graft rejection. We observed that the elevation of IL-4, IL-8, and IL-10 correlated with graft rejection. These cytokines were elevated in samples where HCMV or HHV6 were detected alone or where EBV and HHV7 were co-detected. Interestingly, latent EBV, when detected independently, exhibited an immunomodulatory effect by downregulating cytokine levels. However, in co-detection scenarios with β-herpesviruses, EBV transitioned to a lytic state, also associating with heightened cytokinemia and graft rejection. These findings highlight the complex interactions between the immune response and herpesviruses in transplant recipients. The study advocates for enhanced monitoring of not only EBV and HCMV but also HHV6 and HHV7, providing valuable insights for improved risk assessment and targeted interventions in pediatric SOT recipients.

Intercellular Transport of Viral Proteins

Viruses are vehicles to exchange genetic information and proteins between cells and organisms by infecting their target cells either cell-free, or depending on cell-cell contacts. Several viruses like certain retroviruses or herpesviruses transmit by both mechanisms. However, viruses have also evolved the properties to exchange proteins between cells independent of viral particle formation. This exchange of viral proteins can be directed to target cells prior to infection to interfere with restriction factors and intrinsic immunity, thus, making the target cell prone to infection. However, also bystander cells, e.g. immune cell populations, can be targeted by viral proteins to dampen antiviral responses. Mechanistically, viruses exploit several routes of cell-cell communication to exchange viral proteins like the formation of extracellular vesicles or the formation of long-distance connections like tunneling nanotubes. Although it is known that viral nucleic acids can be transferred between cells as well, this chapter concentrates on viral proteins of human pathogenic viruses covering all Baltimore classes and summarizes our current knowledge on intercellular transport of viral proteins between cells.

Immunity and Immune Evasion Mechanisms of Epstein-Barr Virus

Epstein-Barr virus (EBV) is the first human oncogenic virus to be identified, which evades the body's immune surveillance through multiple mechanisms that allow long-term latent infection. Under certain pathological conditions, EBVs undergo a transition from the latent phase to the lytic phase and cause targeted dysregulation of the host immune system, leading to the development of EBV-related diseases. Therefore, an in-depth understanding of the mechanism of developing an immune response to EBV and the evasion of immune recognition by EBV is important for the understanding of the pathogenesis of EBV, which is of great significance for finding strategies to prevent EBV infection, and developing a therapy to treat EBV-associated diseases. In this review, we will discuss the molecular mechanisms of host immunological responses to EBV infection and the mechanisms of EBV-mediated immune evasion during chronic active infection.

Strategies of Epstein-Barr virus to evade innate antiviral immunity of its human host

Epstein-Barr virus (EBV) is a double-stranded DNA virus of the Herpesviridae family. This virus preferentially infects human primary B cells and persists in the human B cell compartment for a lifetime. Latent EBV infection can lead to the development of different types of lymphomas as well as carcinomas such as nasopharyngeal and gastric carcinoma in immunocompetent and immunocompromised patients. The early phase of viral infection is crucial for EBV to establish latency, but different viral components are sensed by cellular sensors called pattern recognition receptors (PRRs) as the first line of host defense. The efficacy of innate immunity, in particular the interferon-mediated response, is critical to control viral infection initially and to trigger a broad spectrum of specific adaptive immune responses against EBV later. Despite these restrictions, the virus has developed various strategies to evade the immune reaction of its host and to establish its lifelong latency. In its different phases of infection, EBV expresses up to 44 different viral miRNAs. Some act as viral immunoevasins because they have been shown to counteract innate as well as adaptive immune responses. Similarly, certain virally encoded proteins also control antiviral immunity. In this review, we discuss how the virus governs innate immune responses of its host and exploits them to its advantage.

Anti-inflammatory cytokines in sickle cell disease

Sickle cell disease (SCD) is a well-studied monogenetic disease with an established chronic inflammatory component. The paradigm shift towards inflammation has made the pathophysiology of SCD even more complex. Studies have shown that an imbalance between the pro-inflammatory and anti-inflammatory cytokines in SCD exists; however, the reports are skewed toward the pro-inflammatory mediators. We enumerate recent in vitro and in vivo studies on anti-inflammatory cytokines in SCD patients, and discuss the biology of anti-inflammatory cytokines including the already reported IL-2, TGF-β, and IL-10 as well as the recently discovered IL-27, IL-35 and IL-37. This review will improve the understanding of the pathophysiology of SCD and aid in the search of new therapeutic options for patients with SCD.

Viral IL-10 promotes cell proliferation and cell cycle progression via JAK2/STAT3 signaling pathway in nasopharyngeal carcinoma cells

Epstein-Barr virus (EBV) is positively related to the morbidity of nasopharyngeal carcinoma (NPC) in Asia. After infection, EBV can produce several proteins, including viral interleukin-10 (vIL-10). But the mechanism by which vIL-10 contributes to NPC cell proliferation and cell cycle progression is not well understood. In this study, EBV negative and positive cell lines, and the JAK2/STAT3 signal pathway inhibitor AG490 were used to illustrate the role of vIL-10 in NPC. Cell proliferation and cell cycle were measured by CCK-8 and flow cytometry. The expression levels of related protein were measured by Western blotting. High concentrations of vIL-10 and IL-6 were found in the EBV positive patients. The expression level of IL-6 was positively related to the presence of concentration of vIL-10. vIL-10 can promote cancer cell proliferation and G1 to S phase transmission via upregulating the IL-6 protein level by activating the JAK2/STAT3 signal pathway. Furthermore, EBV can induce the formation of cytotoxic T cells, whereas vIL-10 can block the function of cytotoxic T cells. Taken together, these results suggest that vIL-10 promotes cell proliferation and cell cycle progression via JAK2/STAT3 signaling pathway in NPC.

Chronic viral infections in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Background and main text

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex and controversial clinical condition without having established causative factors. Increasing numbers of cases during past decade have created awareness among patients as well as healthcare professionals. Chronic viral infection as a cause of ME/CFS has long been debated. However, lack of large studies involving well-designed patient groups and validated experimental set ups have hindered our knowledge about this disease. Moreover, recent developments regarding molecular mechanism of pathogenesis of various infectious agents cast doubts over validity of several of the past studies.

Conclusions

This review aims to compile all the studies done so far to investigate various viral agents that could be associated with ME/CFS. Furthermore, we suggest strategies to better design future studies on the role of viral infections in ME/CFS.

Interplay Between Microenvironmental Abnormalities and Infectious Agents in Tumorigenesis

Emerging evidence has shown that the cell of microenvironmental abnormalities is a key factor that controls many cellular physiological processes including cellular communication, homing, proliferation, and survival. Given its central regulatory role, it is therefore not surprising that it is widely exploited by infectious agents for inducing pathogenesis. In the past decade, a number of oncogenic pathogens including viruses, bacteria, and parasites are demonstrated to take advantage of the tumor microenvironmental factors including hypoxia, oxidative stress, and cytokines, to create an extracellular environment more favorable for pathogen survival and propagation and escape from the host immune surveillance. Here we summarize and highlight the current understanding of the interplay between common tumor microenvironmental factors and oncogenic pathogens in promoting tumorigenesis.

Epstein-Barr virus and rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases, with a 0.5% worldwide prevalence. The cause of RA remains unknown, however both genetic and environmental factors may contribute to its development. Among these is the Epstein-Barr virus (EBV). Here, we discuss several aspects of the close relationship between EBV and RA. Patients with RA have impaired control of EBV infection. Indeed, they have high titres of antibodies against EBV antigens. Their peripheral blood T lymphocytes are less efficient at controlling the outgrowth of EBV-infected B cells. RA patients have more EBV-infected B cells than normal controls, leading to a 10-fold systemic EBV overload. Post-transplant lymphoproliferative disorder (PTLPD) is a polyclonal EBV-positive B lymphocyte proliferation, which can evolve into an EBV-positive B cell lymphoma. RA patients also have an increased risk of developing EBV-associated lymphoproliferative disorder (LPD). Hence the need to monitor EBV load when treating RA patients with immunosuppressors. EBV, a widespread virus, highly recognized by antibodies but never eliminated, is an ideal candidate to trigger chronic immune complex disease. Anti-EBV antibody responses should be considered as one of the chronic autoantibody responses linked to the development of RA, in the same way as anti-citrullinated protein antibodies.

Possible Mechanisms of Acquisition of Herpesvirus Virokines

The genomes of certain types of human and primate herpesviruses contain functional homologs of important host cytokines (IL-6, IL-17, and IL-10), or so-called virokines. Virokines can interact with immune cell receptors, transmit a signal to them, and thus switch the type of immune response that facilitates viral infection development. In this work, we have summarized possible ways of virokine origin and proposed an evolutionary scenario of virokine acquisition with involvement of retroviral coinfection of the host. This scenario is probably valid for vIL-6 of HHV-8 and MRV-5 viruses, vIL-17 of HVS virus, and vIL-10 of HHV-4, Bonobo-HV, RhLCV, and BaLCV viruses. The ability to acquire cytokine genes allows herpesviruses to implement unique strategies of avoiding the immune response and provides them an evolutionary advantage: more than 90% of the host population can be chronically infected with different herpesviruses. It is possible that the biological success of herpesviruses can be partially due to their cooperation with another group of viruses. This hypothesis emphasizes the importance of studies on the reciprocal influence of pathogens on their coinfection, as well as their impact on the host organism.

Immune camouflage: relevance to vaccines and human immunology

High strain sequence variability, interference with innate immune mechanisms, and epitope deletion are all examples of strategies that pathogens have evolved to subvert host defenses. To this list we would add another strategy: immune camouflage. Pathogens whose epitope sequences are cross-conserved with multiple human proteins at the TCR-facing residues may be exploiting “ignorance and tolerance," which are mechanisms by which mature T cells avoid immune responses to self-antigens. By adopting amino acid configurations that may be recognized by autologous regulatory T cells, pathogens may be actively suppressing protective immunity. Using the new JanusMatrix TCR-homology-mapping tool, we have identified several such ‘camouflaged’ tolerizing epitopes that are present in the viral genomes of pathogens such as emerging H7N9 influenza. Thus in addition to the overall low number of T helper epitopes that is present in H7 hemaglutinin (as described previously, see http://dx.doi.org/10.4161/hv.24939), the presence of such tolerizing epitopes in H7N9 could explain why, in recent vaccine trials, whole H7N9-HA was poorly immunogenic and associated with low seroconversion rates (see http://dx.doi.org/10.4161/hv.28135). In this commentary, we provide an overview of the immunoinformatics process leading to the discovery of tolerizing epitopes in pathogen genomic sequences, provide a brief summary of laboratory data that validates the discovery, and point the way forward. Removal of viral, bacterial and parasite tolerizing epitopes may permit researchers to develop more effective vaccines and immunotherapeutics in the future.

Lipoxins exert antiangiogenic and anti-inflammatory effects on Kaposi's sarcoma cells

Lipoxin A4 (LXA4) is an endogenously produced host molecule with anti-inflammatory resolution effects. Previous studies demonstrated it to be involved in anti-vascular endothelial growth factor (VEGF)-mediated angiogenesis and in a possible anticancer role via interaction with its receptor, lipoxin A 4 receptor (ALXR). Here, we examined the effects of LXA4 and its epimer 15-epi-LXA4 in inhibiting proinflammatory and angiogenic functions in a human Kaposi's sarcoma tumor-derived cell line (KS-IMM). KS-IMM cells expressed increased levels of inflammatory cyclooxygenase 2 (COX-2) and 5-lipoxygenase (5-LO) pathway enzymes when compared with human microvascular dermal endothelial cells (HMVEC-d). KS-IMM cells secreted high levels of prostaglandin E2 (PGE2) and chemotactic leukotriene B4 (LTB4). Treatment with LXA4 or 15-epi-LXA4 effectively reduced the levels of COX-2, 5-LO proteins, and secretion of PGE2 and LTB4 in KS-IMM cells. LXA4 or 15-epi-LXA4 treatment also decreased secretion of proinflammatory interleukin 6 (IL-6) and IL-8 cytokines but induced the secretion of anti-inflammatory IL-10. LXA4 treatment reduced the phosphorylation of VEGF receptor (VEGFR) and ephrin family receptor tyrosine kinases. LXA4 treatment effectively induced dephosphorylation of multiple cellular kinases such as Focal Adhesion Kinase, Protein kinase B, nuclear factor kappa-light-chain-enhancer of activated B cells, and Extracellular signal-regulated kinases (ERK)1/2, and reduced angiogenic factor VEGF-C secretion in KS cells. LX treatment drastically induced the Src-homology 2 domain-containing phosphatase tyrosine (Y542) phosphatase and reduced VEGFR-2 phosphorylation at sites Y1059, Y1175, and Y1212. Treatment of KS-IMM cells with LXA4 resulted in selective localization of VEGFR-2 in nonlipid raft (non-LR) and ALXR to LR fractions. These results demonstrated that LXA4 or 15-epi-LXA4 induce anti-inflammatory and antiangiogenic effects in KS cells and suggest that treatment with LXs is an attractive novel strategy against KS.

Epstein-Barr virus infection in chronically inflamed periapical granulomas

Periapical granulomas are lesions around the apex of a tooth caused by a polymicrobial infection. Treatment with antibacterial agents is normally performed to eliminate bacteria from root canals; however, loss of the supporting alveolar bone is typically observed, and tooth extraction is often selected if root canal treatment does not work well. Therefore, bacteria and other microorganisms could be involved in this disease. To understand the pathogenesis of periapical granulomas more precisely, we focused on the association with Epstein-Barr virus (EBV) using surgically removed periapical granulomas (n = 32). EBV DNA was detected in 25 of 32 periapical granulomas (78.1%) by real-time PCR, and the median number of EBV DNA copies was approximately 8,688.01/μg total DNA. In contrast, EBV DNA was not detected in healthy gingival tissues (n = 10); the difference was statistically significant according to the Mann-Whitney U test (p = 0.0001). Paraffin sections were also analyzed by in situ hybridization to detect EBV-encoded small RNA (EBER)-expressing cells. EBER was detected in the cytoplasm and nuclei of B cells and plasma cells in six of nine periapical granulomas, but not in healthy gingival tissues. In addition, immunohistochemical analysis for latent membrane protein 1 (LMP-1) of EBV using serial tissue sections showed that LMP-1-expressing cells were localized to the same areas as EBER-expressing cells. These data suggest that B cells and plasma cells in inflamed granulomas are a major source of EBV infection, and that EBV could play a pivotal role in controlling immune cell responses in periapical granulomas.

Targeting of viral interleukin-10 with an antibody fragment specific to damaged arthritic cartilage improves its therapeutic potency

INTRODUCTION

We previously demonstrated that a single-chain fragment variable (scFv) specific to collagen type II (CII) posttranslationally modified by reactive oxygen species (ROS) can be used to target anti-inflammatory therapeutics specifically to inflamed arthritic joints. The objective of the present study was to demonstrate the superior efficacy of anti-inflammatory cytokines when targeted to inflamed arthritic joints by the anti-ROS modified CII (anti-ROS-CII) scFv in a mouse model of arthritis.

METHODS

Viral interleukin-10 (vIL-10) was fused to anti-ROS-CII scFv (1-11E) with a matrix-metalloproteinase (MMP) cleavable linker to create 1-11E/vIL-10 fusion. Binding of 1-11E/vIL-10 to ROS-CII was determined by enzyme-linked immunosorbent assay (ELISA), Western blotting, and immune-staining of arthritic cartilage, whereas vIL-10 bioactivity was evaluated in vitro by using an MC-9 cell-proliferation assay. Specific in vivo localization and therapeutic efficacy of 1-11E/vIL-10 was tested in the mouse model of antigen-induced arthritis.

RESULTS

1-11E/vIL-10 bound specifically to ROS-CII and to damaged arthritic cartilage. Interestingly, the in vitro vIL-10 activity in the fusion protein was observed only after cleavage with MMP-1. When systemically administered to arthritic mice, 1-11E/vIL-10 localized specifically to the arthritic knee, with peak accumulation observed after 3 days. Moreover, 1-11E/vIL-10 reduced inflammation significantly quicker than vIL-10 fused to the control anti-hen egg lysozyme scFv (C7/vIL10).

CONCLUSIONS

Targeted delivery of anti-inflammatory cytokines potentiates their anti-arthritic action in a mouse model of arthritis. Our results further support the hypothesis that targeting biotherapeutics to arthritic joints may be extended to include anti-inflammatory cytokines that lack efficacy when administered systemically.

Kaposi's sarcoma-associated herpesvirus induces rapid release of angiopoietin-2 from endothelial cells

Kaposi sarcoma-associated herpesvirus (KSHV) stimulates proliferation, angiogenesis, and inflammation to promote Kaposi sarcoma (KS) tumor growth, which involves various growth factors and cytokines. Previously, we found that KSHV infection of human umbilical vein endothelial cells (HUVECs) induces a transcriptional induction of the proangiogenic and proinflammatory cytokine angiopoietin-2 (Ang-2). Here, we report that KSHV induces rapid release of Ang-2 that is presynthesized and stored in the Weibel-Palade bodies (WPB) of endothelial cells upon binding to its integrin receptors. Blocking viral binding to integrins inhibits Ang-2 release. KSHV binding activates the integrin tyrosine kinase receptor signaling pathways, leading to tyrosine phosphorylation of focal adhesion kinase (FAK), the tyrosine kinase Src, and the Calα2 subunit of the l-type calcium channel to trigger rapid calcium (Ca(2+)) influx. Pretreatment of endothelial cells with specific inhibitors of protein tyrosine kinases inhibits KSHV-induced Ca(2+) influx and Ang-2 release. Inhibition of Ca(2+) mobilization with calcium channel blockers also inhibits Ang-2 release. Thus, the interaction between KSHV and its integrin receptors plays a key role in regulating rapid Ang-2 release from endothelial cells. This finding highlights a novel mechanism of viral induction of angiogenesis and inflammation, which might play important roles in the early event of KS tumor development.

Professional antigen presenting cells in human herpesvirus 8 infection

Professional antigen presenting cells (APC), i.e., dendritic cells (DC), monocytes/macrophages, and B lymphocytes, are critically important in the recognition of an invading pathogen and presentation of antigens to the T cell-mediated arm of immunity. Human herpesvirus 8 (HHV-8) is one of the few human viruses that primarily targets these APC for infection, altering their cytokine profiles, manipulating their surface expression of MHC molecules, and altering their ability to activate HHV-8-specific T cells. This could be why T cell responses to HHV-8 antigens are not very robust. Of these APC, only B cells support complete, lytic HHV-8 infection. However, both complete and abortive virus replication cycles in APC could directly affect viral pathogenesis and progression to Kaposi's sarcoma (KS) and HHV-8-associated B cell cancers. In this review, we discuss the effects of HHV-8 infection on professional APC and their relationship to the development of KS and B cell lymphomas.

Human herpesviridae methods of natural killer cell evasion

Human herpesviruses cause diseases of considerable morbidity and mortality, ranging from encephalitis to hematologic malignancies. As evidence emerges about the role of innate immunity and natural killer (NK) cells in the control of herpesvirus infection, evidence of viral methods of innate immune evasion grows as well. These methods include interference with the ligands on infected cell surfaces that bind NK cell activating or inhibitory receptors. This paper summarizes the most extensively studied NK cell receptor/ligand pairs and then describes the methods of NK cell evasion used by all eight herpesviruses through these receptors and ligands. Although great strides have been made in elucidating their mechanisms, there is still a disparity between viruses in the amount of knowledge regarding innate immune evasion. Further research of herpesvirus innate immune evasion can provide insight for circumventing viral mechanisms in future therapies.