Acute human herpesvirus-6A infection of human mesothelial cells modulates HLA molecules

Gestational Viral Infections: Role of Host Immune System

Viral infections in pregnancy are major causes of maternal and fetal morbidity and mortality. Infections can develop in the neonate transplacentally, perinatally, or postnatally (from breast milk or other sources) and lead to different clinical manifestations, depending on the viral agent and the gestational age at exposure. Viewing the peculiar tolerogenic status which characterizes pregnancy, viruses could exploit this peculiar immunological status to spread or affect the maternal immune system, adopting several evasion strategies. In fact, both DNA and RNA virus might have a deep impact on both innate and acquired immune systems. For this reason, investigating the interaction with these pathogens and the host's immune system during pregnancy is crucial not only for the development of most effective therapies and diagnosis but mostly for prevention. In this review, we will analyze some of the most important DNA and RNA viruses related to gestational infections.

Role of HLA-G in Viral Infections

The human leukocyte antigen (HLA)-G is a non-classical HLA class I molecule, which has distinct features to classical HLA-A, -B, -C antigens, such as a low polymorphism, different splice variants, highly restricted, tightly regulated expression and immune modulatory properties. HLA-G expression in tumor cells and virus-infected cells, as well as the release of soluble HLA-G leads to escape from host immune surveillance. Increased knowledge of the link between HLA-G expression, viral infection and disease progression is urgently required, which highlights the possible use of HLA-G as novel diagnostic and prognostic biomarker for viral infections, but also as therapeutic target. Therefore, this review aims to summarize the expression, regulation, function and impact of HLA-G in the context of different viral infections including virus-associated cancers. The characterization of HLA-G-driven immune escape mechanisms involved in the interactions between host cells and viruses might result in the design of novel immunotherapeutic strategies targeting HLA-G and/or its interaction with its receptors on immune effector cells.

Insights into the knowledge of complex diseases: Environmental infectious/toxic agents as potential etiopathogenetic factors of systemic sclerosis

Systemic sclerosis (SSc) is a connective tissue disease secondary to three cardinal pathological features: immune-system alterations, diffuse microangiopathy, and fibrosis involving the skin and internal organs. The etiology of SSc remains quite obscure; it may encompass multiple host genetic and environmental -infectious/chemical-factors. The present review focused on the potential role of environmental agents in the etiopathogenesis of SSc based on epidemiological, clinical, and laboratory investigations previously published in the world literature. Among infectious agents, some viruses that may persist and reactivate in infected individuals, namely human cytomegalovirus (HCMV), human herpesvirus-6 (HHV-6), and parvovirus B19 (B19V), and retroviruses have been proposed as potential causative agents of SSc. These viruses share a number of biological activities and consequent pathological alterations, such as endothelial dysfunction and/or fibroblast activation. Moreover, the acute worsening of pre-existing interstitial lung involvement observed in SSc patients with symptomatic SARS-CoV-2 infection might suggest a potential role of this virus in the overall disease outcome. A variety of chemical/occupational agents might be regarded as putative etiological factors of SSc. In this setting, the SSc complicating silica dust exposure represents one of the most promising models of study. Considering the complexity of SSc pathogenesis, none of suggested causative factors may explain the appearance of the whole SSc; it is likely that the disease is the result of a multifactorial and multistep pathogenetic process. A variable combination of potential etiological factors may modulate the appearance of different clinical phenotypes detectable in individual scleroderma patients. The in-deep investigations on the SSc etiopathogenesis may provide useful insights in the broad field of human diseases characterized by diffuse microangiopathy or altered fibrogenesis.

Evasion of the Host Immune Response by Betaherpesviruses

The human immune system boasts a diverse array of strategies for recognizing and eradicating invading pathogens. Human betaherpesviruses, a highly prevalent subfamily of viruses, include human cytomegalovirus (HCMV), human herpesvirus (HHV) 6A, HHV-6B, and HHV-7. These viruses have evolved numerous mechanisms for evading the host response. In this review, we will highlight the complex interplay between betaherpesviruses and the human immune response, focusing on protein function. We will explore methods by which the immune system first responds to betaherpesvirus infection as well as mechanisms by which viruses subvert normal cellular functions to evade the immune system and facilitate viral latency, persistence, and reactivation. Lastly, we will briefly discuss recent advances in vaccine technology targeting betaherpesviruses. This review aims to further elucidate the dynamic interactions between betaherpesviruses and the human immune system.

Late-onset intrauterine growth restriction and HHV-6 infection: A pilot study

Late-onset Intrauterine growth restriction (IUGR) refers to impaired growth and development of the fetus, characterized by placental morphological abnormalities that affect the fetus's supply of nutrients. Human leukocyte antigen-G (HLA-G) is physiologically expressed during pregnancy, but decreased in normal placenta during the last weeks of gestation possibly inducing childbirth. Several viruses involved in congenital infection, such as herpesviruses, exploit HLA-G expression as an immune-escape mechanism. To date, despite different congenital herpetic infections having been associated with late IUGR, no direct implication of Human herpesvirus 6 (HHV-6) infection has been reported. We evaluated HLA-G expression and HHV-6 infection in 11 placentas from late-onset IUGR newborns and 11 placentas from uncomplicated pregnancies by histopathological and immunohistochemistry analysis. We found higher levels of HLA-G expression and HHV-6 presence in IUGR placenta samples compared with control placenta samples. We report HHV-6 staining in IUGR placenta samples, characterized by high HLA-G expression. These preliminary data suggest a possible involvement of HHV-6 infection in HLA-G deregulation that might affect vessel remodeling and prevent the correct pregnancy outcome in the IUGR condition.

The U94 Gene of Human Herpesvirus 6: A Narrative Review of Its Role and Potential Functions

Human herpesvirus 6 (HHV-6) is a β-herpesvirus that is highly prevalent in the human population. HHV-6 comprises two recognized species (HHV-6A and HHV-6B). Despite different cell tropism and disease association, HHV-6A/B show high genome homology and harbor the conserved U94 gene, which is limited to HHV-6 and absent in all the other human herpesviruses. U94 has key functions in the virus life cycle and associated diseases, having demonstrated or putative roles in virus replication, integration, and reactivation. During natural infection, U94 elicits an immune response, and the prevalence and extent of the anti-U94 response are associated with specific diseases. Notably, U94 can entirely reproduce some virus effects at the cell level, including inhibition of cell migration, induction of cytokines and HLA-G expression, and angiogenesis inhibition, supporting a direct U94 role in the development of HHV-6-associated diseases. Moreover, specific U94 properties, such as the ability to modulate angiogenesis pathways, have been exploited to counteract cancer development. Here, we review the information available on this key HHV-6 gene, highlighting its potential uses.

The P2X7 Receptor 489C>T Gain of Function Polymorphism Favors HHV-6A Infection and Associates With Female Idiopathic Infertility

The P2X7 receptor (P2X7R) is an ATP-gated ion channel known for its proinflammatory activity. Despite its participation in host defense against pathogens, the role played in viral infections, notably those caused by herpes viruses, has been seldom studied. Here we investigated the effect of P2X7R expression on human herpes virus 6 A (HHV-6A) infection of P2X7R-expressing HEK293 cells. We show that functional P2X7R increases while its blockade decreases viral load. Interestingly, HHV-6A infection was enhanced in HEK293 cells transfected with P2X7R cDNA bearing the gain of function 489C>T SNP (rs208294, replacing a histidine for tyrosine at position 155). The P2X7R 489C>T polymorphism correlated with HHV-6A infection also in a cohort of 50 women affected with idiopathic infertility, a condition previously shown to correlate with HHV-6A infection. None of the infertile women infected by HHV-6A was homozygote for 489CC genotype, while on the contrary HHV-6A infection significantly associated with the presence of the rs208294 allele. Levels of soluble human leukocyte antigen G (sHLA-G), a factor promoting embryo implant, measured in uterine flushings negatively correlated with the 489TT genotype and HHV-6A infection, while proinflammatory cytokines interleukins 1α (IL-1α), 1β (IL-1β), and 8 (IL-8) positively correlated with both the 489T allele presence and viral infection. Taken together these data point to the P2X7R as a new therapeutic target to prevent HHV-6A infection and the associated infertility.

HHV-6A Infection of Endometrial Epithelial Cells Affects miRNA Expression and Trophoblast Cell Attachment

We recently reported that human herpesvirus 6 (HHV-6) infection is frequently present in endometrial tissue of women with unexplained infertility, and that virus infection induces a profound remodulation of miRNA expression in human cells of different origin. Since specific miRNA patterns have been associated with specific pregnancy outcomes, we aimed to analyze the impact of HHV-6A infection on miRNAs expression and trophoblast receptivity in human endometrial cells. To this purpose, a human endometrial cell line (HEC-1A) was infected with HHV-6A and analyzed for alterations in the expression of miRNAs and for permissiveness to the attachment of a human choriocarcinoma trophoblast cell line (JEG-3). The results showed that HHV-6A infection of endometrial cells up-modulates miR22 (26-fold), miR15 (19.5-fold), and miR196-5p (12.1 fold), that are correlated with implant failure, and down-modulates miR18 (11.4 fold), miR101-3p (4.6 fold), miR181-5p (4.9 fold), miR92 (3.3 fold), and miR1207-5p (3.9 fold), characterized by a low expression in preeclampsia. Moreover, HHV-6A-infected endometrial cells infected resulted less permissive to the attachment of trophoblast cells. In conclusion, collected data suggest that HHV-6A infection could modify miRNA expression pattern and control of trophoblast cell adhesion of endometrial cells, undermining a correct trophoblast cell attachment on endometrial cells.

HHV-6A Infection and Systemic Sclerosis: Clues of a Possible Association

Systemic sclerosis (SSc) is an autoimmune disease characterized by vasculopathy, excessive extracellular matrix deposition, and fibrosis of the skin and internal organs. Several infectious agents, including human herpesvirus-6 (HHV-6), have been suggested as possible triggering factors, but a direct association is still missing. We characterized 26 SSc patients for the presence of HHV-6 in tissues and blood, the anti-HHV-6 response, HLA-G plasma levels, and KIR typing. Given the prominent role of endothelial cells (EC) in SSc pathogenesis, along with HHV-6 tropism for EC, we also investigated the expression of pro-fibrosis factors in HHV-6 infected EC. Results showed the presence of HHV-6A in skin biopsies, and an increased virus load was associated with disease severity and poor natural killer (NK) response against the virus, particularly in subjects exhibiting a KIR2 phenotype. HLA-G plasma levels were significantly higher in HHV-6A/B-KIR2 positive SSc patients and in vitro HHV-6A infection-induced pro-fibrosis factors expression in EC, supporting its role in the development of the fibrosing process. Our data suggest an association between virus infection/reactivation and disease, opening the way to future studies to understand the mechanisms by which HHV-6A might contribute to the multifactorial pathogenesis of SSc.

HHV-6A infection induces amyloid-beta expression and activation of microglial cells

BACKGROUND

The control of viral infections in the brain involves the activation of microglial cells, the macrophages of the brain that are constantly surveying the central nervous system, and the production of amyloid-beta (Aβ) as an anti-microbial molecule. Recent findings suggest a possible implication of HHV-6A in AD. We evaluated the effect of HHV-6A infection on microglial cell expression Aβ and the activation status, determined by TREM2, ApoE, cytokines, and tau expression.

METHODS

We have infected microglial cells (HMC3, ATCC®CRL-3304), in monolayer and human peripheral blood monocyte-derived microglia (PBM-microglia) spheroid 3D model, with HHV-6A (strain U1102) cell-free virus inocula with 100 genome equivalents per 1 cell. We collected the cells 1, 3, 7, and 14 days post-infection (d.p.i.) and analyzed them for viral DNA and RNA, ApoE, Aβ (1-40, 1-42), tau, and phospho-tau (Threonine 181) by real-time immunofluorescence and cytokines by immunoenzymatic assay.

RESULTS

We observed a productive infection by HHV-6A. The expression of Aβ 1-42 increased from 3 d.p.i., while no significant induction was observed for Aβ 1-40. The HHV-6A infection induced the activation (TREM2, IL-1beta, ApoE) and migration of microglial cells. The secretion of tau started from 7 d.p.i., with an increasing percentage of the phosphorylated form.

CONCLUSIONS

In conclusion, microglial cells are permissive to HHV-6A infection that induces the expression of Aβ and an activation status. Meanwhile, we hypothesize a paracrine effect of HHV-6A infection that activates and induces microglia migration to the site of infection.

Pleural effusions induced by human herpesviruses in the immunocompetent host

METHODS

A computer-based search of the English literature for articles relative to Human Herpesviruses (HHVs) infection and pleural effusions (PEs) in the immunocompetent host was performed in PubMed and Scopus. The reference lists of the retrieved articles were also reviewed for relevant articles.

RESULTS

A total of 20 articles satisfied the selection criteria and were included in the study. In the majority of the articles, PEs were reported as clinical complications of systemic HHV-induced infection. The frequency of HHVs within the reported cases was five for HHV-1/2, one for HHV-3, six for HHV-4, six for HHV-5 and one for HHV-6. One case involved HHV-4 and HHV-5 co-infection. No case of HHV-7 or HHV-8 related PE in the immunocompetent host was retrieved.

CONCLUSIONS

Pleural effusions in the immunocompetent host occur in severe viral infections and can be due to comorbidities (or septic complications) or due to the direct HHV pathogenicity although research relative to the susceptibility of pleural mesothelial cells to HHV infection is lacking. HHV pathogenicity needs to be studied further as it could explain undiagnosed PEs.

Human Herpesvirus 6A and 6B inhibit in vitro angiogenesis by induction of Human Leukocyte Antigen G

We have previously reported that human herpesvirus 6 (HHV-6) infection of endothelial cells (ECs) induces the loss of angiogenic properties, through the expression of HHV-6 U94, possibly associated to the release of a soluble mediator. It is also known that the soluble isoform of HLA-G exhibits an anti-angiogenic function, important in implantation, transplantation and neoplastic development. In this study, we analyzed the expression of HLA-G in HHV-6 infected ECs, showing that both HHV-6A and HHV-6B infection induce a potent up-modulation of HLA-G, including both membrane and soluble isoforms. Interestingly, HHV-6A and HHV-6B induced different isoforms of HLA-G. The virus-induced increase of HLA-G was likely due to the expression of the U94 viral gene, that by itself was able to reproduce the effect of whole virus. The effect of U94 was mediated by human transcription factor ATF3, that induced HLA-G activation by recognizing a consensus sequence on its promoter. Virus-induced inhibition of ECs angiogenic ability directly correlated to HLA-G expression and release, and the addition of anti-HLA-G antibody restored the angiogenic properties of HHV6-infected ECs. The induction of HLA-G expression in ECs might represent an important mediator of HHV-6 induced effects.

HLA and killer cell immunoglobulin-like receptor (KIRs) genotyping in patients with acute viral encephalitis

Introduction

The HLA genes, as well as the innate immune KIR genes, are considered relevant determinants of viral outcomes but no study, to our knowledge, has evaluated their role in the clinical setting of acute viral encephalitis.

Results

Subjects with acute viral encephalitis in comparison to subjects without acute viral encephalitis showed a significantly higher frequency of 2DL1 KIR gene and AA KIR haplotypes and of HLA-C2 and HLA-A-Bw4 alleles. Subjects without acute viral encephalitis showed a higher frequency of interaction between KIR2DL2 and HLAC1. Multiple logistic regression analysis showed the detrimental effect of HLA-A haplotype and HLA-C1, HLA-A-BW4 HLA-B-BW4^T alleles, whereas multiple logistic regression showed a protective effect of AB+BB KIR haplotype and a detrimental effect of interaction between KIR3DL1 and HLA-A-Bw4.

Discussion

Our findings of a lower frequency of activating receptors in patients with acute encephalitis compared to controls could result in a less efficient response of NK cells. This finding could represent a possible pathogenetic explanation of susceptibility to acute symptomatic encephalitis in patients with viral infection from potentially responsible viruses such as Herpes virus.

Materials and Methods

30 Consecutive patients with symptomatic acute viral encephalitis and as controls, 36 consecutive subjects without acute encephalitis were analyzed. The following KIR genes were analyzed, KIR2DL1, 2DL2, 2DL3, 2DL5, 3DL1, 3DL2, 3DL3, 2DL4, 2DS1, 2DS2, 2DS3, 2DS4, 2DS5, 3DS1, 2 pseudogenes (2DP1 and 3DP1) and the common variants of KIR2DL5 (KIR2DL5A, KIR2DL5B).

The Interplay between Natural Killer Cells and Human Herpesvirus-6

Human Herpesvirus 6 (HHV-6) is a set of two closely related herpes viruses known as HHV-6A and HHV-6B. Both are lymphotropic viruses that establish latency in the host. The ability to evade the immune responses of effector cells is likely a major factor contributing to the development of a persistent HHV-6A/B (collectively termed HHV-6) infection. Natural killer (NK) cells are lymphocytes that, along with neutrophils and monocytes/macrophages, participate in the critical innate immune response during viral infections, but can also mediate the antigen-specific memory responses generally associated with adaptive immunity. NK cells compose the first barrier that viruses must break through to continue replication and dissemination, and a weak NK cell response may predispose an individual to chronic viral infections. Both HHV-6A and HHV-6B can interfere with NK cell-mediated anti-viral responses but the mechanisms by which each of these viruses affect NK cell activity differs. In this review, we will explore the nuanced relationships between the two viruses and NK cells, discussing, in addition, relevant disease associations.

HHV-6A/6B Infection of NK Cells Modulates the Expression of miRNAs and Transcription Factors Potentially Associated to Impaired NK Activity

Natural killer (NK) cells have a critical role in controlling virus infections, and viruses have evolved several mechanisms to escape NK cell functions. In particular, Human herpesvirus 6 (HHV-6) is associated with diseases characterized by immune dysregulation and has been reported to infect NK cells. We recently found that HHV-6 in vitro infection of human thyroid follicular epithelial cells and T-lymphocytes modulates several miRNAs associated with alterations in immune response. Since miRNAs are key regulators of many immune pathways, including NK cell functions, we aimed to study the impact of HHV-6A and -6B in vitro infection on the intracellular mediators correlated to NK cell function. To this purpose, a human NK cell line (NK-92) was infected in vitro with HHV-6A or 6B and analyzed for alterations in the expression of miRNAs and transcription factors. The results showed that both viruses establish lytic replication in NK-92 cells, as shown by the presence of viral DNA, expression of lytic transcripts and antigens, and by the induction of an evident cytopathic effect. Notably, both viruses, although with species-specific differences, induced significant modifications in miRNA expression of miRNAs known for their role in NK cell development, maturation and effector functions (miR-146, miR-155, miR-181, miR-223), and on at least 13 miRNAs with recognized role in inflammation and autoimmunity. Also the expression of transcription factors was significantly modified by HHV-6A/6B infection, with an early increase of ATF3, JUN and FOXA2 by both species, whereas HHV-6A specifically induced a 15-fold decrease of POU2AF1, and HHV-6B an increase of FOXO1 and a decrease of ESR1. Overall, our data show that HHV-6A and -6B infections have a remarkable effect on the expression of miRNAs and transcription factors, which might be important in the induction of NK cell function impairment, virus escape strategies and related pathologies.