Rotavirus activates lymphocytes from non-obese diabetic mice by triggering toll-like receptor 7 signaling and interferon production in plasmacytoid dendritic cells

Does the Human Gut Virome Contribute to Host Health or Disease?

The human gastrointestinal (GI) tract harbors eukaryotic and prokaryotic viruses and their genomes, metabolites, and proteins, collectively known as the "gut virome". This complex community of viruses colonizing the enteric mucosa is pivotal in regulating host immunity. The mechanisms involved in cross communication between mucosal immunity and the gut virome, as well as their relationship in health and disease, remain largely unknown. Herein, we review the literature on the human gut virome's composition and evolution and the interplay between the gut virome and enteric mucosal immunity and their molecular mechanisms. Our review suggests that future research efforts should focus on unraveling the mechanisms of gut viruses in human homeostasis and pathophysiology and on developing virus-prompted precision therapies.

Mild-to-moderate COVID-19 does not predispose to the development of autoimmune rheumatic diseases or autoimmune-based thrombosis

An infection with severe acute respiratory syndrome coronavirus (SARS-CoV-2) may have a significant impact on the human immune system. Interactions between the virus and defence mechanisms may promote the development of autoimmune processes which manifest as antinuclear antibody (ANA) synthesis. Since many different viruses are suspected to take part in the pathogenesis of different systemic autoimmune rheumatic diseases (SARDs), we examined whether coronavirus disease 2019 convalescents who suffer from mild to moderate disease have a higher risk of developing ANA and anti-β2-glicoprotein I IgG antibodies (β2 GPI). In a retrospective study, we examined 294 adults among volunteer blood donors divided into convalescents (N = 215) and healthy controls (N = 79). For ANA detection, we used line-blotting, a type of indirect immunofluorescence assay (IF), to determine antigenic specificity and ELISA for β2 GPI. We found a lower incidence of ANA in convalescents than in healthy controls, with the majority of these antibodies directed to antigens with no known clinical significance. Additionally, no participants were positive for β2 GPI in either group. Our results show that COVID-19 with mild to moderate symptoms in the generally healthy population does not induce the development of ANA or anti-β2 GPI antibodies for at least 6 months following the disease.

Immunomodulation by Enteric Viruses

Enteric viruses display intricate adaptations to the host mucosal immune system to successfully reproduce in the gastrointestinal tract and cause maladies ranging from gastroenteritis to life-threatening disease upon extraintestinal dissemination. However, many viral infections are asymptomatic, and their presence in the gut is associated with an altered immune landscape that can be beneficial or adverse in certain contexts. Genetic variation in the host and environmental factors including the bacterial microbiota influence how the immune system responds to infections in a remarkably viral strain-specific manner. This immune response, in turn, determines whether a given virus establishes acute versus chronic infection, which may have long-lasting consequences such as susceptibility to inflammatory disease. In this review, we summarize our current understanding of the mechanisms involved in the interaction between enteric viruses and the immune system that underlie the impact of these ubiquitous infectious agents on our health.

Steady-state memory-phenotype conventional CD4+ T cells exacerbate autoimmune neuroinflammation in a bystander manner via the Bhlhe40/GM-CSF axis

Memory-phenotype (MP) CD4⁺ T cells are a substantial population of conventional T cells that exist in steady-state mice, yet their immunological roles in autoimmune disease remain unclear. In this work, we unveil a unique phenotype of MP CD4⁺ T cells determined by analyzing single-cell transcriptomic data and T cell receptor (TCR) repertoires. We found that steady-state MP CD4⁺ T cells in the spleen were composed of heterogeneous effector subpopulations and existed regardless of germ and food antigen exposure. Distinct subpopulations of MP CD4⁺ T cells were specifically activated by IL-1 family cytokines and STAT activators, revealing that the cells exerted TCR-independent bystander effector functions similar to innate lymphoid cells. In particular, CCR6^high subpopulation of MP CD4⁺ T cells were major responders to IL-23 and IL-1β without MOG_35-55 antigen reactivity, which gave them pathogenic Th17 characteristics and allowed them to contribute to autoimmune encephalomyelitis. We identified that Bhlhe40 in CCR6^high MP CD4⁺ T cells as a key regulator of GM-CSF expression through IL-23 and IL-1β signaling, contributing to central nervous system (CNS) pathology in experimental autoimmune encephalomyelitis. Collectively, our findings reveal the clearly distinct effector-like heterogeneity of MP CD4⁺ T cells in the steady state and indicate that CCR6^high MP CD4⁺ T cells exacerbate autoimmune neuroinflammation via the Bhlhe40/GM-CSF axis in a bystander manner.

Molecular Mimicry Analyses Unveiled the Human Herpes Simplex and Poxvirus Epitopes as Possible Candidates to Incite Autoimmunity

Clinical epidemiological studies have reported that viral infections cause autoimmune pathology in humans. Host-pathogen protein sequences and structure-based molecular mimicry cause autoreactive T cells to cross-activate. The aim of the current study was to implement immunoinformatics approaches to infer sequence- and structure-based molecular mimicry between viral and human proteomic datasets. The protein sequences of all the so far known human-infecting viruses were obtained from the VIPR database, and complete human proteome data were retrieved from the NCBI repository. Based on a predefined, stringent threshold of comparative sequence analyses, 24 viral proteins were identified with significant sequence similarity to human proteins. PathDIP identified the enrichment of these homologous proteins in nine metabolic pathways with a p-value < 0.0001. Several viral and human mimic epitopes from these homologous proteins were predicted as strong binders of human HLA alleles, with IC50 < 50 nM. Downstream molecular docking analyses identified that lead virus-human homologous epitopes feasibly interact with HLA and TLR4 types of immune receptors. The vast majority of these top-hit homolog epitopic peptides belong to the herpes simplex and poxvirus families. These lead epitope biological sequences and 3D structural-based molecular mimicry may be promising for interpreting herpes simplex virus and poxvirus infection-mediated autoimmune disorders in humans.

Re-Examining Rotavirus Innate Immune Evasion: Potential Applications of the Reverse Genetics System

Rotaviruses represent one of the most successful pathogens in the world, with high infectivity and efficient transmission between the young of many animal species, including humans. To overcome host defenses, rotaviruses have evolved a plethora of strategies to effectively evade the innate immune response, establish initial infection in the small intestine, produce progeny, and shed into the environment. Previously, studying the roles and relative contributions of specific rotaviral factors in innate immune evasion had been challenging without a plasmid-only reverse genetics system. Although still in its infancy, current reverse genetics technology will help address important research questions regarding rotavirus innate immune evasion, host range restriction, and viral pathogenesis. In this review, we summarize the current knowledge about the antiviral host innate immune defense mechanisms, countermeasures of rotavirus-encoded factors, and strategies to better understand these interactions using the rotavirus reverse genetics system.

Microbial (co)infections: Powerful immune influencers

It is well established that by modulating various immune functions, host infection may alter the course of concomitant inflammatory diseases, of both infectious and autoimmune etiologies. Beyond the major impact of commensal microbiota on the immune status, host exposure to viral, bacterial, and/or parasitic microorganisms also dramatically influences inflammatory diseases in the host, in a beneficial or harmful manner. Moreover, by modifying pathogen control and host tolerance to tissue damage, a coinfection can profoundly affect the development of a concomitant infectious disease. Here, we review the diverse mechanisms that underlie the impact of (co)infections on inflammatory disorders. We discuss epidemiological studies in the context of the hygiene hypothesis and shed light on the sometimes dual impact of germ exposure on human susceptibility to inflammatory disease. We then summarize the immunomodulatory mechanisms at play, which can involve pleiotropic effects of immune players and discuss the possibility to harness pathogen-derived compounds to the host benefit.

Role of nucleic acid sensing in the pathogenesis of type 1 diabetes

During infections, nucleic acids of pathogens are also engaged in recognition via several exogenous and cytosolic pattern recognition receptors, such as the toll-like receptors, retinoic acid inducible gene-I-like receptors, and nucleotide-binding and oligomerization domain-like receptors. The binding of the pathogen-derived nucleic acids to their corresponding sensors initiates certain downstream signaling cascades culminating in the release of type-I interferons (IFNs), especially IFN-α and other cytokines to induce proinflammatory responses towards invading pathogens leading to their clearance from the host. Although these sensors are hardwired to recognize pathogen associated molecular patterns, like viral and bacterial nucleic acids, under unusual physiological conditions, such as excessive cellular stress and increased apoptosis, endogenous self-nucleic acids like DNA, RNA, and mitochondrial DNA are also released. The presence of these self-nucleic acids in extranuclear compartments or extracellular spaces or their association with certain proteins sometimes leads to the failure of discriminating mechanisms of nucleic acid sensors leading to proinflammatory responses as seen in autoimmune disorders, like systemic lupus erythematosus, psoriasis and to some extent in type 1 diabetes (T1D). This review discusses the involvement of various nucleic acid sensors in autoimmunity and discusses how aberrant recognition of self-nucleic acids by their sensors activates the innate immune responses during the pathogenesis of T1D.

The dark side of the gut: Virome-host interactions in intestinal homeostasis and disease

The diverse enteric viral communities that infect microbes and the animal host collectively constitute the gut virome. Although recent advances in sequencing and analysis of metaviromes have revealed the complexity of the virome and facilitated discovery of new viruses, our understanding of the enteric virome is still incomplete. Recent studies have uncovered how virome-host interactions can contribute to beneficial or detrimental outcomes for the host. Understanding the complex interactions between enteric viruses and the intestinal immune system is a prerequisite for elucidating their role in intestinal diseases. In this review, we provide an overview of the enteric virome composition and summarize recent findings about how enteric viruses are sensed by and, in turn, modulate host immune responses during homeostasis and disease.

Rotavirus and Type 1 Diabetes-Is There a Connection? A Synthesis of the Evidence

Although the etiology of type 1 diabetes (T1D) is not well understood, it is believed to comprise both genetic and environmental factors. Viruses are the most well studied environmental trigger, and there is a small but growing body of research on the potential influence of rotavirus on T1D. Rotavirus infections were initially identified as possible triggers of T1D given similarities between viral peptide sequences and T1D autoantigen peptide sequences. Furthermore, rotavirus infection has been shown to modify T1D risk in T1D-prone mice. However, research into associations of rotavirus infections with T1D development in humans have yielded mixed findings and suggested interactions with age and diet. As global availability of rotavirus vaccines increases, recent studies have assessed whether rotavirus vaccination modifies T1D development, finding null or protective associations. Overall, evidence to date suggests a possible triggering relationship between some wild-type rotavirus infections and T1D, but the potential effect of rotavirus vaccination remains unclear.

Effects of Intestinal Fungi and Viruses on Immune Responses and Inflammatory Bowel Diseases

The intestinal microbiota comprises diverse fungal and viral components, in addition to bacteria. These microbes interact with the immune system and affect human physiology. Advances in metagenomics have associated inflammatory and autoimmune diseases with alterations in fungal and viral species in the gut. Studies of animal models have found that commensal fungi and viruses can activate host-protective immune pathways related to epithelial barrier integrity, but can also induce reactions that contribute to events associated with inflammatory bowel disease. Changes in our environment associated with modernization and the COVID-19 pandemic have exposed humans to new fungi and viruses, with unknown consequences. We review the lessons learned from studies of animal viruses and fungi commonly detected in the human gut and how these might affect health and intestinal disease.

Interferon α Enhances B Cell Activation Associated With FOXM1 Induction: Potential Novel Therapeutic Strategy for Targeting the Plasmablasts of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease. It is characterized by the production of various pathogenic autoantibodies and is suggested to be triggered by increased type I interferon (IFN) signature. Previous studies have identified increased plasmablasts in the peripheral blood of SLE patients. The biological characteristics of SLE plasmablasts remain unknown, and few treatments that target SLE plasmablasts have been applied despite the unique cellular properties of plasmablasts compared with other B cell subsets and plasma cells. We conducted microarray analysis of naïve and memory B cells and plasmablasts (CD38+CD43+ B cells) that were freshly isolated from healthy controls and active SLE (n = 4, each) to clarify the unique biological properties of SLE plasmablasts. The results revealed that all B cell subsets of SLE expressed more type I IFN-stimulated genes. In addition, SLE plasmablasts upregulated the expression of cell cycle-related genes associated with higher FOXM1 and FOXM1-regulated gene expression levels than that in healthy controls. This suggests that a causative relationship exists between type I IFN priming and enhanced proliferative capacity through FOXM1. The effects of pretreatment of IFNα on B cell activation and FOXM1 inhibitor FDI-6 on B cell proliferation and survival were investigated. Pretreatment with IFNα promoted B cell activation after stimulation with anti-IgG/IgM antibody. Flow cytometry revealed that pretreatment with IFNα preferentially enhanced the Atk and p38 pathways after triggering B cell receptors. FDI-6 inhibited cell division and induced apoptosis in activated B cells. These effects were pronounced in activated B cells pretreated with interferon α. This study can provide better understanding of the pathogenic mechanism of interferon-stimulated genes on SLE B cells and an insight into the development of novel therapeutic strategies.

Toll-like receptor 7 deficiency suppresses type 1 diabetes development by modulating B-cell differentiation and function

Innate immunity mediated by Toll-like receptors (TLRs), which can recognize pathogen molecular patterns, plays a critical role in type 1 diabetes development. TLR7 is a pattern recognition receptor that senses single-stranded RNAs from viruses and host tissue cells; however, its role in type 1 diabetes development remains unclear. In our study, we discovered that Tlr7-deficient (Tlr7-/-) nonobese diabetic (NOD) mice, a model of human type 1 diabetes, exhibited a significantly delayed onset and reduced incidence of type 1 diabetes compared with Tlr7-sufficient (Tlr7+/+) NOD mice. Mechanistic investigations showed that Tlr7 deficiency significantly altered B-cell differentiation and immunoglobulin production. Moreover, Tlr7-/- NOD B cells were found to suppress diabetogenic CD4+ T-cell responses and protect immunodeficient NOD mice from developing diabetes induced by diabetogenic T cells. In addition, we found that Tlr7 deficiency suppressed the antigen-presenting functions of B cells and inhibited cytotoxic CD8+ T-cell activation by downregulating the expression of both nonclassical and classical MHC class I (MHC-I) molecules on B cells. Our data suggest that TLR7 contributes to type 1 diabetes development by regulating B-cell functions and subsequent interactions with T cells. Therefore, therapeutically targeting TLR7 may prove beneficial for disease protection.

Gut eukaryotic virome in colorectal carcinogenesis: Is that a trigger?

The human gut microbiota is composed of bacteria and viruses that might be associated with colorectal cancer (CRC) onset and progression. Indeed, although viral infections have been reported to be the primary trigger in many diseases, the role of eukaryotic viruses populating the gut mucosa during early colorectal carcinogenesis is underinvestigated. Human eukaryotic viruses in the gut were found to induce alterations of the immune homeostasis so that some viral-dependent mechanisms likely able to induce DNA alterations in the bowel wall have been proposed, although no demonstration is available yet. However, thanks to the latest advancements in computational biology and the implementation of the bioinformatic pipelines, the option of establishing a direct causative link between intestinal virome and CRC will be possible soon, hopefully paving the way to innovative therapeutic strategies blocking or reverting the CRC pathogenesis.

The gliadin p31-43 peptide: Inducer of multiple proinflammatory effects

Coeliac disease (CD) is the prototype of an inflammatory chronic disease induced by food. In this context, gliadin p31-43 peptide comes into the spotlight as an important player of the inflammatory/innate immune response to gliadin in CD. The p31-43 peptide is part of the p31-55 peptide from α-gliadins that remains undigested for a long time, and can be present in the small intestine after ingestion of a gluten-containing diet. Different biophysical methods and molecular dynamic simulations have shown that p31-43 spontaneously forms oligomeric nanostructures, whereas experimental approaches using in vitro assays, mouse models, and human duodenal tissues have shown that p31-43 is able to induce different forms of cellular stress by driving multiple inflammatory pathways. Increased proliferative activity of the epithelial cells in the crypts, enterocyte stress, activation of TG2, induction of Ca²⁺, IL-15, and NFκB signaling, inhibition of CFTR, alteration of vesicular trafficking, and activation of the inflammasome platform are some of the biological effects of p31-43, which, in the presence of appropriate genetic susceptibility and environmental factors, may act together to drive CD.

Association Between Rotavirus Vaccination and Type 1 Diabetes in Children

IMPORTANCE

Because rotavirus infection is a hypothesized risk factor for type 1 diabetes, live attenuated rotavirus vaccination could increase or decrease the risk of type 1 diabetes in children.

OBJECTIVE

To examine whether there is an association between rotavirus vaccination and incidence of type 1 diabetes in children aged 8 months to 11 years.

DESIGN, SETTING, AND PARTICIPANTS

A retrospective cohort study of 386 937 children born between January 1, 2006, and December 31, 2014, was conducted in 7 US health care organizations of the Vaccine Safety Datalink. Eligible children were followed up until a diagnosis of type 1 diabetes, disenrollment, or December 31, 2017.

EXPOSURES

Rotavirus vaccination for children aged 2 to 8 months. Three exposure groups were created. The first group included children who received all recommended doses of rotavirus vaccine by 8 months of age (fully exposed to rotavirus vaccination). The second group had received some, but not all, recommended rotavirus vaccines (partially exposed to rotavirus vaccination). The third group did not receive any doses of rotavirus vaccines (unexposed to rotavirus vaccination).

MAIN OUTCOMES AND MEASURES

Incidence of type 1 diabetes among children aged 8 months to 11 years. Type 1 diabetes was identified by International Classification of Diseases codes: 250.x1, 250.x3, or E10.xx in the outpatient setting. Cox proportional hazards regression models were used to analyze time to type 1 diabetes incidence from 8 months to 11 years. Hazard ratios and 95% CIs were calculated. Models were adjusted for sex, race/ethnicity, birth year, mother's age, birth weight, gestational age, number of well-child visits, and Vaccine Safety Datalink site.

RESULTS

In a cohort of 386 937 children (51.1% boys and 41.9% non-Hispanic white), 360 169 (93.1%) were fully exposed to rotavirus vaccination, 15 765 (4.1%) were partially exposed to rotavirus vaccination, and 11 003 (2.8%) were unexposed to rotavirus vaccination. Children were followed up a median of 5.4 years (interquartile range, 3.8-7.8 years). The total person-time follow-up in the cohort was 2 253 879 years. There were 464 cases of type 1 diabetes in the cohort, with an incidence rate of 20.6 cases per 100 000 person-years. Compared with children unexposed to rotavirus vaccination, the adjusted hazard ratio was 1.03 (95% CI, 0.62-1.72) for children fully exposed to rotavirus vaccination and 1.50 (95% CI, 0.81-2.77) for children partially exposed to rotavirus vaccination.

CONCLUSIONS AND RELEVANCE

The findings of this study suggest that rotavirus vaccination does not appear to be associated with type 1 diabetes in children.

Rotavirus and autoimmunity

Rotavirus, a major etiological agent of acute diarrhea in children worldwide, has historically been linked to autoimmunity. In the last few years, several physiopathological approaches have been proposed to explain the leading mechanism triggering autoimmunity, from the old concept of molecular mimicry to the emerging theory of bystander activation and break of tolerance. Epidemiological and immunological data indicate a strong link between rotavirus infection and two of the autoimmune pathologies with the highest incidence: celiac disease and diabetes. The role for current oral rotavirus vaccines is now being elucidated, with a so far positive protective association demonstrated.

The Role of Innate Immunity in Regulating Rotavirus Replication, Pathogenesis, and Host Range Restriction and the Implications for Live Rotaviral Vaccine Development

Rotaviruses (RVs) are important causative agents of viral gastroenteritis in the young of most mammalian species studied, including humans, in which they are the most important cause of severe gastroenteritis worldwide despite the availability of several safe and effective vaccines. Replication of RVs is restricted in a host species-specific manner, and this barrier is determined predominantly by the host interferon (IFN) signaling and the ability of different RV strains to successfully negate IFN activation and amplification pathways. In addition, viral attachment to the target intestinal epithelial cells also regulates host range restriction. Several studies have focused on the role of the innate immune response in regulating RV replication and pathogenesis. The knowledge accrued from these efforts is likely to result in rational attenuation of RV vaccines to closely match circulating (and host species-matched) virus strains. In this chapter, we review prevalent models of RV interactions with innate immune factors, viral strategies employed to regulate their function, and the implications of these findings for improved RV vaccine development.

Viruses and Autoimmunity: A Review on the Potential Interaction and Molecular Mechanisms

For a long time, viruses have been shown to modify the clinical picture of several autoimmune diseases, including type 1 diabetes (T1D), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Sjögren’s syndrome (SS), herpetic stromal keratitis (HSK), celiac disease (CD), and multiple sclerosis (MS). Best examples of viral infections that have been proposed to modulate the induction and development of autoimmune diseases are the infections with enteric viruses such as Coxsackie B virus (CVB) and rotavirus, as well as influenza A viruses (IAV), and herpesviruses. Other viruses that have been studied in this context include, measles, mumps, and rubella. Epidemiological studies in humans and experimental studies in animal have shown that viral infections can induce or protect from autoimmunopathologies depending on several factors including genetic background, host-elicited immune responses, type of virus strain, viral load, and the onset time of infection. Still, data delineating the clear mechanistic interaction between the virus and the immune system to induce autoreactivity are scarce. Available data indicate that viral-induced autoimmunity can be activated through multiple mechanisms including molecular mimicry, epitope spreading, bystander activation, and immortalization of infected B cells. Contrarily, the protective effects can be achieved via regulatory immune responses which lead to the suppression of autoimmune phenomena. Therefore, a better understanding of the immune-related molecular processes in virus-induced autoimmunity is warranted. Here we provide an overview of the current understanding of viral-induced autoimmunity and the mechanisms that are associated with this phenomenon.

Oligosaccharides Modulate Rotavirus-Associated Dysbiosis and TLR Gene Expression in Neonatal Rats

Colonization of the gut in early life can be altered through multiple environmental factors. The present study aimed to investigate the effects of 2'-fucosyllactose (2'-FL), a mixture of short-chain galactooligosaccharides/long-chain fructooligosaccharides (scGOS/lcFOS) 9:1 and their combination (scGOS/lcFOS/2'-FL) on dysbiosis induced during rotavirus (RV) diarrhea in neonatal rats, elucidating crosstalk between bacteria and the immune system. The dietary interventions were administered daily by oral gavage at days 2-8 of life in neonatal Lewis rats. On day 5, RV SA11 was intragastrically delivered to induce infection and diarrhea assessment, microbiota composition, and gene expression of Toll-like receptors (TLRs) in the small intestine were studied. All dietary interventions showed reduction in clinical variables of RV-induced diarrhea. RV infection increased TLR2 expression, whereas 2'-FL boosted TLR5 and TLR7 expressions and scGOS/lcFOS increased that of TLR9. RV-infected rats displayed an intestinal dysbiosis that was effectively prevented by the dietary interventions, and consequently, their microbiota was more similar to microbiota of the noninfected groups. The preventive effect of 2'-FL, scGOS/lcFOS, and their combination on dysbiosis associated to RV diarrhea in rats could be due to changes in the crosstalk between gut microbiota and the innate immune system.

The Intestinal Virome and Immunity

The composition of the human microbiome is considered a major source of interindividual variation in immunity and, by extension, susceptibility to diseases. Intestinal bacteria have been the major focus of research. However, diverse communities of viruses that infect microbes and the animal host cohabitate the gastrointestinal tract and collectively constitute the gut virome. Although viruses are typically investigated as pathogens, recent studies highlight a relationship between the host and animal viruses in the gut that is more akin to host-microbiome interactions and includes both beneficial and detrimental outcomes for the host. These viruses are likely sources of immune variation, both locally and extraintestinally. In this review, we describe the components of the gut virome, in particular mammalian viruses, and their ability to modulate host responses during homeostasis and disease.

NLRC5 deficiency has a moderate impact on immunodominant CD8+ T-cell responses during rotavirus infection of adult mice

The NOD-like receptor (NLR) family plays an important role in innate immunity. Class II transactivator and NOD-like receptor caspase activation and recruitment domain CARD containing 5 (NLRC5) are unusual members of the NLR family that instead of recognizing pathogen-associated or damage-associated molecular patterns, form enhanceosomes with adaptor molecules and modulate major histocompatibility complex (MHC) class II and MHC class I expression, respectively. While NLRC5 has been shown to play a role during intracellular pathogen infection and tumor cell immune evasion, its role in regulating antigen-specific CD8⁺ T-cell responses at the intestinal mucosa has not been investigated. Here, we take advantage of the rotavirus model in adult mice to dissect the impact of NLRC5 on CD8⁺ T-cell responses to this viral infection at the gut mucosa. We show that while Nlrc5^-/- mice exhibited normal proportions of T-cell subpopulations in the intraepithelial and lamina propria compartments, these mice had decreased baseline MHC class I expression on various immune cells in the lamina propria. Upon rotavirus infection, Nlrc5 deficiency resulted in impaired H2-K^b -restricted antigen-specific CD8⁺ T-cell responses, which were recapitulated in mice deficient for Nlrc5 within the dendritic cell compartment. The impaired CD8⁺ T-cell response in Nlrc5^-/- mice was not significant enough to impact viral titers, suggesting compensation in Nlrc5^-/- mice, perhaps as a result of higher numbers of activated B cells in the mesenteric lymph nodes and normal rotavirus-specific immunoglobulin A responses. Collectively, our results demonstrate a minor role for NLRC5 in modulating H2-K^b -restricted antigen-specific CD8⁺ T-cell responses in the small intestine during rotavirus infection in adult mice.

Diagnosis of gluten-related enteropathy in a newborn: how and when?

AIM

To analyze the development of gliadin-specific immune responses in children with a genetic risk for CD and to determine whether these could be detected before the clinical onset of the disease by using immunological tests.

BACKGROUND

Clinical manifestations of celiac disease (CD) in the first year of life is uncommon, which is due to the suboptimal sensitivity of tissue transglutaminase IgA antibodies (tTG-IgA) at this age and other possible causes of malabsorption in infants. The development of Deamidate gliadin peptide-specific antibodies (in particular DGP-IgG) in young children was poorly considered in the CD diagnosis.

METHODS

We conducted a retrospective cross-sectional study on children between one month and forty-eight months of life, which performed in our health center from 2016 to 2018. Three hundred and fifty children were selected according to strict inclusion criteria: positive for HLA-DQA1 and DQB1 alleles, positive anti tTG-IgA/IgG and/or positive DGP-IgG/IgA. Eighty-two children were selected and divided into two different groups of patients: Group one (forty newborns under twenty-four months of life) and Group two (children from twenty-five months to 48 months of life).

RESULTS

Anti-DGP-IgG antibodies precede anti tTG-IgA seroconversion in children under two years in 80% of cases. Anti-DGP-IgG positive patients had milder symptomatic forms of CD than anti tTG-IgA positive children, characterized by gastrointestinal symptoms in the presence of normal growth, normal serum iron, and low MCH level. At tTG-IgA seroconversion, children present gastrointestinal clinical forms associated with impaired growth. The combined use of tTG-IgA and DGP-IgG antibodies upgrade the diagnostic sensitivity from 50% to 92%.

CONCLUSION

Anti-DGP-IgG antibodies precede tTG-IgA seroconversion in newborns and identified two distinct clinical phenotypes. At this point, if you wanted to test your newborn patients for CD serology, how would you proceed?

P31-43, an undigested gliadin peptide, mimics and enhances the innate immune response to viruses and interferes with endocytic trafficking: a role in celiac disease

Celiac disease (CD) is an autoimmune disease characterized by inflammation of the intestinal mucosa due to an immune response to wheat gliadins. Some gliadin peptides are resistant to intestinal digestion (e.g., A-gliadin P31–43) and induce a stress/innate immune response, but the reason why they are dangerous in the intestines of patients with CD is unknown. In the present study, P31–43 activated IFN-α, a mediator of the innate immune response in CD, in the intestine of subjects with CD and an enterocyte cell line, CaCo-2. P31–43 cooperated with a viral ligand to activate the TLR7 pathway by interfering with endocytic trafficking. Based on these results, the vesicular pathway regulates the innate/inflammatory response to viral ligands and bioactive dietary peptides. Suggesting that together with viral infections, alimentary proteins able to mimic and potentiate the innate immune response to viruses, can trigger an autoimmune disease such as CD.

Enteric Virome Sensing-Its Role in Intestinal Homeostasis and Immunity

Pattern recognition receptors (PRRs) sensing commensal microorganisms in the intestine induce tightly controlled tonic signaling in the intestinal mucosa, which is required to maintain intestinal barrier integrity and immune homeostasis. At the same time, PRR signaling pathways rapidly trigger the innate immune defense against invasive pathogens in the intestine. Intestinal epithelial cells and mononuclear phagocytes in the intestine and the gut-associated lymphoid tissues are critically involved in sensing components of the microbiome and regulating immune responses in the intestine to sustain immune tolerance against harmless antigens and to prevent inflammation. These processes have been mostly investigated in the context of the bacterial components of the microbiome so far. The impact of viruses residing in the intestine and the virus sensors, which are activated by these enteric viruses, on intestinal homeostasis and inflammation is just beginning to be unraveled. In this review, we will summarize recent findings indicating an important role of the enteric virome for intestinal homeostasis as well as pathology when the immune system fails to control the enteric virome. We will provide an overview of the virus sensors and signaling pathways, operative in the intestine and the mononuclear phagocyte subsets, which can sense viruses and shape the intestinal immune response. We will discuss how these might interact with resident enteric viruses directly or in context with the bacterial microbiome to affect intestinal homeostasis.

MHC class I expression in intestinal cells is reduced by rotavirus infection and increased in bystander cells lacking rotavirus antigen

Detection of viral infection by host cells leads to secretion of type I interferon, which induces antiviral gene expression. The class I major histocompatibility complex (MHCI) is required for viral antigen presentation and subsequent infected cell killing by cytotoxic T lymphocytes. STAT1 activation by interferon can induce NLRC5 expression, promoting MHCI expression. Rotavirus, an important pathogen, blocks interferon signalling through inhibition of STAT1 nuclear translocation. We assessed MHCI expression in HT-29 intestinal epithelial cells following rotavirus infection. MHCI levels were upregulated in a partially type I interferon-dependent manner in bystander cells lacking rotavirus antigen, but not in infected cells. MHCI and NLRC5 mRNA expression also was elevated in bystander, but not infected, cells, suggesting a transcriptional block in infected cells. STAT1 was activated in bystander and infected cells, but showed nuclear localisation in bystander cells only. Overall, the lack of MHCI upregulation in rotavirus-infected cells may be at least partially due to rotavirus blockade of interferon-induced STAT1 nuclear translocation. The reduced MHCI protein levels in infected cells support the existence of an additional, non-transcriptional mechanism that reduces MHCI expression. It is possible that rotavirus also may suppress MHCI expression in vivo, which might limit T cell-mediated killing of rotavirus-infected enterocytes.

Rotavirus infection

Rotavirus infections are a leading cause of severe, dehydrating gastroenteritis in children <5 years of age. Despite the global introduction of vaccinations for rotavirus over a decade ago, rotavirus infections still result in >200,000 deaths annually, mostly in low-income countries. Rotavirus primarily infects enterocytes and induces diarrhoea through the destruction of absorptive enterocytes (leading to malabsorption), intestinal secretion stimulated by rotavirus non-structural protein 4 and activation of the enteric nervous system. In addition, rotavirus infections can lead to antigenaemia (which is associated with more severe manifestations of acute gastroenteritis) and viraemia, and rotavirus can replicate in systemic sites, although this is limited. Reinfections with rotavirus are common throughout life, although the disease severity is reduced with repeat infections. The immune correlates of protection against rotavirus reinfection and recovery from infection are poorly understood, although rotavirus-specific immunoglobulin A has a role in both aspects. The management of rotavirus infection focuses on the prevention and treatment of dehydration, although the use of antiviral and anti-emetic drugs can be indicated in some cases.

Effects of Lactobacillus rhamnosus GG on the maturation and differentiation of dendritic cells in rotavirus-infected mice

Rotavirus-related diarrhoea is considered one of the most important diseases in field animal production. In addition to the classic vaccine strategy, a number of studies have utilised probiotics, such as Lactobacillus rhamnosus GG (LGG), to prevent rotavirus-induced diarrhoea. Although it has been partially revealed that Toll-like receptors (TLRs) are involved in the LGG-mediated protection against rotavirus infection, the details of the underlying immunologic mechanisms remain largely unknown. In this study, three-to-four-week-old female BALB/c mice were divided into three groups and orally administered phosphate buffered saline (PBS), PBS plus rotavirus or LGG plus rotavirus, respectively. The differentiation and maturation of dendritic cells (DCs) were then determined by FACS, the expression levels of TLR-3 and nuclear factor kappa beta (NF-κB) were evaluated using real time PCR, and the production of inflammatory cytokines in mesenteric lymph nodes (MLNs) were determined by ELISA. The results demonstrated that rotavirus infection significantly increased the percentage of CD11c⁺CD11b⁺CD8a^- DCs and decreased the percentage of CD11c⁺CD11b^-CD8a⁺ DCs in MLNs. By contrast, the presence of LGG significantly decreased the percentage of CD11c⁺CD11b⁺CD8a^- DCs and increased the percentage of CD11c⁺CD11b^-CD8a⁺ DCs, which indicates that the differentiation of DCs is involved in the protective effects of LGG. Rotavirus infection also resulted in the increased expression of surface markers such as CD40, CD80 and MHC-II in DCs, and the administration of LGG significantly increased the expression level further. The mRNA levels of TLR-3 and NF-κB in the intestine and MLNs were also significantly increased in the presence of rotavirus, which was further increased in the presence of LGG. The production of inflammatory cytokines was also determined, and the results showed that rotavirus caused the increased production of interleukin (IL)-12 and tumour necrosis factor alpha; this effect was further enhanced by LGG. Meanwhile, although rotavirus infection led to the increased production of IL-6 and IL-10, the presence of LGG significantly decreased the mRNA levels of these cytokines. By contrast, rotavirus infection resulted in the decreased production of interferon gamma (IFN-γ), and the administration of LGG significantly increased the levels of IFN-γ. Taken together, the protective effects of LGG were partially due to the modulation of the differentiation and maturation of DCs, the increased production of TLR-3 and NF-κB, and the modulation of inflammatory cytokines.

Type 1 Interferon in the Human Intestine-A Co-ordinator of the Immune Response to the Microbiota

The human gut is in constant complex interaction with the external environment. Although much is understood about the composition and function of the microbiota, much remains to be learnt about the mechanisms by which these organisms interact with the immune system in health and disease. Type 1 interferon (T1IFN), a ubiquitous and pleiotropic family of cytokines, is a critical mediator of the response to viral, bacterial, and other antigens sampled in the intestine. Although inflammation is enhanced in mouse model of colitis when T1IFN signaling is lost, the action of T1IFN is context specific and can be pro- or anti-inflammatory. In humans, T1IFN has been used to treat inflammatory diseases, including multiple sclerosis and inflammatory bowel disease but intestinal inflammation can also develop after the administration of T1IFN. Recent findings indicate that "tonic" or "endogenous" T1IFN, induced by signals from the commensal microbiota, modulates the local signaling environment to prime the intestinal mucosal immune system to determine later responses to pathogens and commensal organisms. This review will summarize the complex immunological effects of T1IFN and recent the role of T1IFN as a mediator between the microbiota and the mucosal immune system, highlighting human data wherever possible. It will discuss what we can learn from clinical experiences with T1IFN and how the T1IFN pathway may be manipulated in the future to maintain mucosal homeostasis.

Environmental Basis of Autoimmunity

The three common themes that underlie the induction and perpetuation of autoimmunity are genetic predisposition, environmental factors, and immune regulation. Environmental factors have gained much attention for their role in triggering autoimmunity, with increasing evidence of their influence as demonstrated by epidemiological studies, laboratory research, and animal studies. Environmental factors known to trigger and perpetuate autoimmunity include infections, gut microbiota, as well as physical and environmental agents. To address these issues, we will review major potential mechanisms that underlie autoimmunity including molecular mimicry, epitope spreading, bystander activation, polyclonal activation of B and T cells, infections, and autoinflammatory activation of innate immunity. The association of the gut microbiota on autoimmunity will be particularly highlighted by their interaction with pharmaceutical agents that may lead to organ-specific autoimmunity. Nonetheless, and we will emphasize this point, the precise mechanism of environmental influence on disease pathogenesis remains elusive.

Innate Viral Receptor Signaling Determines Type 1 Diabetes Onset

Heritable susceptibility of the autoimmune disorder, type 1 diabetes (T1D), only partially equates for the incidence of the disease. Significant evidence attributes several environmental stressors, such as vitamin D deficiency, gut microbiome, dietary antigens, and most notably virus infections in triggering the onset of T1D in these genetically susceptible individuals. Extensive epidemiological and clinical studies have provided credibility to this causal relationship. Infection by the enterovirus, coxsackievirus B, has been closely associated with onset of T1D and is considered a significant etiological agent for disease induction. Recognition of viral antigens via innate pathogen-recognition receptors induce inflammatory events which contribute to autoreactivity of pancreatic self-antigens and ultimately the destruction of insulin-secreting beta cells. The activation of these specific innate pathways and expression of inflammatory molecules, including type I and III interferon, prime the immune system to elicit either a protective regulatory response or a diabetogenic effector response. Therefore, sensing of viral antigens by retinoic acid-inducible gene I-like receptors and toll-like receptors may be detrimental to inducing autoreactivity initiated by viral stress and resulting in T1D.

The viral paradigm in type 1 diabetes: Who are the main suspects?

Type 1 diabetes (T1D) is an autoimmune disease characterized by the loss of pancreatic beta cells in the islets of Langerhans. Although genetic predisposition plays an important role in T1D development, studies of identical twins suggest that environmental factors such as viruses and other pathogens may be critical triggers either through direct cytolytic effect and gradual beta cell destruction, or by bystander activation of the immune system. In addition, viruses may circumvent the host immune response and have the capacity to establish chronic lifelong infections. The association of various viral infections with the induction of T1D has been extensively studied at the serological and epidemiological level. However, there is still little evidence from studies of human pancreas to confirm their presence or a causal role in disease pathogenesis. In this review, we identify possible suspects for viral triggers of disease and explain their potential roles in the "viral paradigm" of T1D.

Rotavirus acceleration of type 1 diabetes in non-obese diabetic mice depends on type I interferon signalling

Rotavirus infection is associated with childhood progression to type 1 diabetes. Infection by monkey rotavirus RRV accelerates diabetes onset in non-obese diabetic (NOD) mice, which relates to regional lymph node infection and a T helper 1-specific immune response. When stimulated ex vivo with RRV, plasmacytoid dendritic cells (pDCs) from naïve NOD mice secrete type I interferon, which induces the activation of bystander lymphocytes, including islet-autoreactive T cells. This is our proposed mechanism for diabetes acceleration by rotaviruses. Here we demonstrate bystander lymphocyte activation in RRV-infected NOD mice, which showed pDC activation and strong upregulation of interferon-dependent gene expression, particularly within lymph nodes. The requirement for type I interferon signalling was analysed using NOD mice lacking a functional type I interferon receptor (NOD.IFNAR1(-/-) mice). Compared with NOD mice, NOD.IFNAR1(-/-) mice showed 8-fold higher RRV titers in lymph nodes and 3-fold higher titers of total RRV antibody in serum. However, RRV-infected NOD.IFNAR1(-/-) mice exhibited delayed pDC and lymphocyte activation, no T helper 1 bias in RRV-specific antibodies and unaltered diabetes onset when compared with uninfected controls. Thus, the type I interferon signalling induced by RRV infection is required for bystander lymphocyte activation and accelerated type 1 diabetes onset in genetically susceptible mice.

Systemic features of rotavirus infection

A growing body of evidence warrants a revision of the received/conventional wisdom of rotavirus infection as synonymous with acute gastroenteritis. Rotavirus vaccines have boosted our interest and knowledge of this virus, but also importantly, they may have changed the landscape of the disease. Extraintestinal spread of rotavirus is well documented, and the clinical spectrum of the disease is widening. Furthermore, the positive impact of current rotavirus vaccines in reducing seizure hospitalization rates should prompt a reassessment of the actual burden of extraintestinal manifestations of rotavirus diseases. This article discusses current knowledge of the systemic extraintestinal manifestations of rotavirus infection and their underlying mechanisms, and aims to pave the way for future clinical, public health and research questions.

The role of the innate immune system in destruction of pancreatic beta cells in NOD mice and humans with type I diabetes

Type 1 diabetes (T1D) is an organ-specific autoimmune disease characterized by T cell-mediated destruction of the insulin-producing pancreatic β cells. A combination of genetic and environmental factors eventually leads to the loss of functional β cell mass and hyperglycemia. Both innate and adaptive immunity are involved in the development of T1D. In this review, we have highlighted the most recent findings on the role of innate immunity, especially the pattern recognition receptors (PRRs), in disease development. In murine models and human studies, different PRRs, such as toll-like receptors (TLRs) and nucleotide-binding domain, leucine-rich repeat-containing (or Nod-like) receptors (NLRs), have different roles in the pathogenesis of T1D. These PRRs play a critical role in defending against infection by sensing specific ligands derived from exogenous microorganisms to induce innate immune responses and shape adaptive immunity. Animal studies have shown that TLR7, TLR9, MyD88 and NLPR3 play a disease-predisposing role in T1D, while controversial results have been found with other PRRs, such as TLR2, TLR3, TLR4, TLR5 and others. Human studies also shown that TLR2, TLR3 and TLR4 are expressed in either islet β cells or infiltrated immune cells, indicating the innate immunity plays a role in β cell autoimmunity. Furthermore, some human genetic studies showed a possible association of TLR3, TLR7, TLR8 or NLRP3 genes, at single nucleotide polymorphism (SNP) level, with human T1D. Increasing evidence suggest that the innate immunity modulates β cell autoimmunity. Thus, targeting pathways of innate immunity may provide novel therapeutic strategies to fight this disease.

The virome in host health and disease

The mammalian virome includes diverse commensal and pathogenic viruses that evoke a broad range of immune responses from the host. Sustained viral immunomodulation is implicated in a variety of inflammatory diseases, but also confers unexpected benefits to the host. These outcomes of viral infections are often dependent on host genotype. Moreover, it is becoming clear that the virome is part of a dynamic network of microorganisms that inhabit the body. Therefore, viruses can be viewed as a component of the microbiome, and interactions with commensal bacteria and other microbial agents influence their behavior. This piece is a review of our current understanding of how the virome, together with other components of the microbiome, affects the function of the host immune system to regulate health and disease.

Innate immune responses to rotavirus infection in macrophages depend on MAVS but involve neither the NLRP3 inflammasome nor JNK and p38 signaling pathways

Rotavirus infection is a major cause of life-threatening infantile gastroenteritis. The innate immune system provides an immediate mechanism of suppressing viral replication and is necessary for an effective adaptive immune response. Innate immunity involves host recognition of viral infection and establishment of a powerful antiviral state through the expression of pro-inflammatory cytokines such as type-1 interferon (IFN). Macrophages, the front-line cells of innate immunity, produce IFN and other cytokines in response to viral infection. However, the role of macrophages during rotavirus infection is not well defined. We demonstrate here that RRV rotavirus triggers the production of proinflammatory cytokines from mouse bone marrow-derived macrophages. IFN and antiviral cytokine production was abolished in rotavirus-infected MAVS (-/-) macrophages. This indicates that rotavirus triggers innate immunity in macrophages through RIG-I and/or MDA5 viral recognition, and MAVS signaling is essential for cytokine responses in macrophages. Rotavirus induced IFN expression in both wild type and MDA5 (-/-) macrophages, showing that MDA5 is not essential for IFN secretion following infection, and RIG-I and MDA5 may act redundantly in promoting rotavirus recognition. Interestingly, rotavirus neither stimulated mitogen-activated protein kinases p38 and JNK nor activated the NLRP3 inflammasome, demonstrating that these components might not be involved in innate responses to rotavirus infection in macrophages. Our results indicate that rotavirus elicits intracellular signaling in macrophages, resulting in the induction of IFN and antiviral cytokines, and advance our understanding of the involvement of these cells in innate responses against rotavirus.

Lessons from the mouse: potential contribution of bystander lymphocyte activation by viruses to human type 1 diabetes

Viruses are considered to be potential key modulators of type 1 diabetes mellitus, with several possible mechanisms proposed for their modes of action. Here we discuss the evidence for virus involvement, including pancreatic infection and the induction of T cell-mediated molecular mimicry. A particular focus of this review is the further possibility that virus infection triggers bystander activation of pre-existing autoreactive lymphocytes. In this scenario, the virus triggers dendritic cell maturation and proinflammatory cytokine secretion by engaging pattern recognition receptors. These proinflammatory cytokines provoke bystander autoreactive lymphocyte activation in the presence of cognate autoantigen, which leads to enhanced beta cell destruction. Importantly, this mechanism does not necessarily involve pancreatic virus infection, and its virally non-specific nature suggests that it might represent a means commonly employed by multiple viruses. The ability of viruses specifically associated with type 1 diabetes, including group B coxsackievirus, rotavirus and influenza A virus, to induce these responses is also examined. The elucidation of a mechanism shared amongst several viruses for accelerating progression to type 1 diabetes would facilitate the identification of important targets for disease intervention.

Type I diabetes mellitus: genetic factors and presumptive enteroviral etiology or protection

We review type 1 diabetes and host genetic components, as well as epigenetics and viruses associated with type 1 diabetes, with added emphasis on the enteroviruses, which are often associated with triggering the disease. Genus Enterovirus is classified into twelve species of which seven (Enterovirus A, Enterovirus B, Enterovirus C, and Enterovirus D and Rhinovirus A, Rhinovirus B, and Rhinovirus C) are human pathogens. These viruses are transmitted mainly by the fecal-oral route; they may also spread via the nasopharyngeal route. Enterovirus infections are highly prevalent, but these infections are usually subclinical or cause a mild flu-like illness. However, infections caused by enteroviruses can sometimes be serious, with manifestations of meningoencephalitis, paralysis, myocarditis, and in neonates a fulminant sepsis-like syndrome. These viruses are often implicated in chronic (inflammatory) diseases as chronic myocarditis, chronic pancreatitis, and type 1 diabetes. In this review we discuss the currently suggested mechanisms involved in the viral induction of type 1 diabetes. We recapitulate current basic knowledge and definitions.

MyD88-mediated TLR signaling protects against acute rotavirus infection while inflammasome cytokines direct Ab response

Rotavirus (RV) infects small intestinal epithelial cells, inducing severe diarrhea in children, resulting in over 500,000 deaths annually. Relatively little is known about how innate immunity contains acute infection and drives adaptive immune responses that afford complete clearance of RV and protection against future infection. Hence, we examined the consequence of the absence of MyD88, known to be central to innate immunity, in a mouse model of RV infection. The absence of MyD88, but not combined blockade of IL-1β and IL-18 signaling, resulted in greater infectivity, as reflected by levels of RV in feces, intestinal lysates and viremia. Such increased RV levels correlated with an increase in incidence and duration of diarrhea. Loss of MyD88 also impaired humoral immunity to RV. Specifically, MyD88 knockout generated less RV-specific IgA and exhibited profoundly reduced RV-specific IgG2c/IgG1 ratios suggesting that MyD88 signaling drives RV-induced Th1 responses. A study of MyD88 bone marrow chimeras indicated that MyD88-dependent control of acute RV infection was mediated by both hemopoietic and non-hemopoietic cells, while generation of RV-specific humoral immunity was driven by MyD88 signaling in hemopoietic cells, which reflected the loss of IL-1β and IL-18 expression by these cells. Thus, TLR signaling and inflammasome cytokines drive innate and adaptive immunity to RV.

In silico study of potential autoimmune threats from rotavirus infection

Rotavirus, the major cause of infantile nonbacterial diarrhea, was found to be associated with development of diabetes-associated auto-antibodies. In our study we tried to find out further potential autoimmune threats of this virus using bioinformatics approach. We took rotaviral proteins to study similarity with Homo sapiens proteome and found most conserved structural protein VP6 matches at two regions with ryanodine receptor, an autoimmune target associated with myasthenia gravis. Myasthenia gravis, a chronic neurodegenerative autoimmune disorder with no typical known reason, is characterized by fluctuating muscle weakness which is typically enhanced during muscular effort. Affected patients generate auto antibodies against mainly acetyl choline receptor and sarcoplasmic reticulum calcium-release channel protein ryanodine receptor. Further, we observed that two regions which matched with ryanodine receptor remain conserved in all circulating rotaviral strains and showed significant antigenecity with respect to myasthenia gravis associated HLA haplotypes. Overall, our study detected rotaviral VP6 as a potential threat for myasthenia gravis and enlighten an area of virus associated autoimmune research.