Impaired interferon response in plasmacytoid dendritic cells from children with persistent wheeze.

BACKGROUND: Impaired interferon response and allergic sensitization may contribute to virus-induced wheeze and asthma development in young children. Plasmacytoid dendritic cells (pDCs) play a key role in antiviral immunity as critical producers of type I interferons. pDCs also express the high-affinity IgE receptor through which type I interferon production may be negatively regulated. Whether antiviral function of pDCs is associated with recurrent episodes of wheeze in young children is not well understood. OBJECTIVE: We sought to evaluate the phenotype and function of circulating pDCs in children with a longitudinally defined wheezing phenotype. METHODS: We performed multiparameter flow cytometry on PBMCs from 38 children presenting to the emergency department with an acute episode of respiratory wheeze and 19 controls. RNA sequencing on isolated pDCs from the same individuals was also performed. For each subject, their longitudinal exacerbation phenotype was determined using the Western Australia public hospital database. RESULTS: We observed a significant depletion of circulating pDCs in young children with a persistent phenotype of wheeze. The same individuals also displayed upregulation of the FcεRI on their pDCs. Based on transcriptomic analysis, pDCs from these individuals did not mount a robust systemic antiviral response as observed in children who displayed a nonrecurrent wheezing phenotype. CONCLUSIONS: Our data suggest that circulating pDC phenotype and function are altered in young children with a persistent longitudinal exacerbation phenotype. Expression of high-affinity IgE receptor is increased and their function as major interferon producers is impaired during acute exacerbations of wheeze.

Egg-sensitised infants have elevated CD4+ effector memory T regulatory cells from birth.

BACKGROUND: IgE-mediated sensitisation to egg is common in infants. In some cases, the processes leading to egg sensitisation are established in early life, even before introduction to solid foods. The underlying mechanisms remain poorly understood. METHODS: We performed detailed immune cell phenotyping of peripheral blood mononuclear cells and determined in vitro cytokine responses following allergen specific and non-specific immune stimulation. To determine if unique immune profiles were linked to early-life egg sensitisation, we compared 92 infants at 4-6 months of age, with (EggCAP+, n = 41) and without (EggCAP-, n = 51) early egg sensitisation. Additionally, 47 cord blood samples were analysed. For a subset of participants (n = 39), matching cord blood mononuclear cells were assessed by flow cytometry to establish the impact of IgE sensitisation on immune developmental trajectories. RESULTS: EggCAP+ infants were found to exhibit a unique immune phenotype characterised by increased levels of circulating CD4+ T regulatory cells (Treg), CD4+ effector memory (EM) Treg and increased expression of the IgE receptor, FcεR1, on basophils. The increased CD4+ EM Treg profiles were already present in cord blood samples from EggCAP+ infants. A general Th2-skewing of the immune system was observed based on increased IL-13 production following phytohemagglutinin stimulation and by comparing immune developmental trajectories, EggCAP+ infants displayed an expansion of basophils and reduced levels of CD4- T cells compared to EggCAP- infants. CONCLUSIONS: Immunological profiles associated with egg sensitisation are detectable in infant circulation at 4-6 months of age and at birth. Understanding the immune mechanisms underlying early-life sensitisation could provide important insights for future food allergy prevention strategies.

LPS binding protein and activation signatures are upregulated during asthma exacerbations in children.

Asthma exacerbations in children are associated with respiratory viral infection and atopy, resulting in systemic immune activation and infiltration of immune cells into the airways. The gene networks driving the immune activation and subsequent migration of immune cells into the airways remains incompletely understood. Cellular and molecular profiling of PBMC was employed on paired samples obtained from atopic asthmatic children (n = 19) during acute virus-associated exacerbations and later during convalescence. Systems level analyses were employed to identify coexpression networks and infer the drivers of these networks, and validation was subsequently obtained via independent samples from asthmatic children. During exacerbations, PBMC exhibited significant changes in immune cell abundance and upregulation of complex interlinked networks of coexpressed genes. These were associated with priming of innate immunity, inflammatory and remodelling functions. We identified activation signatures downstream of bacterial LPS, glucocorticoids and TGFB1. We also confirmed that LPS binding protein was upregulated at the protein-level in plasma. Multiple gene networks known to be involved positively or negatively in asthma pathogenesis, are upregulated in circulating PBMC during acute exacerbations, supporting the hypothesis that systemic pre-programming of potentially pathogenic as well as protective functions of circulating immune cells preceeds migration into the airways. Enhanced sensitivity to LPS is likely to modulate the severity of acute asthma exacerbations through exposure to environmental LPS.

Oestrogen amplifies pre-existing atopy-associated Th2 bias in an experimental asthma model.

BACKGROUND: The prevalence and severity of asthma, particularly the most common (atopic) form of the disease, increase amongst females but not males after puberty, and asthma activity also changes throughout the menstrual cycle and during pregnancy. The contribution of female sex hormones to asthma pathogenesis is incompletely understood. OBJECTIVE: To obtain insight into the role of oestrogen (E2) in experimental atopic asthma, and guide future research on sex-related variations in atopic asthma susceptibility/intensity in humans. METHODS: We utilized an experimental model comprising rat strains expressing dichotomous Th2-high vs Th2-low immunophenotypes exemplified by eosinophilia, mirroring differences between human atopics/non-atopics. We compared the efficiency of Th2-associated immunoinflammatory mechanisms, which differed markedly between the two strains, and between sexes in the Th2-high strain, and determined the effects of E2 administration on these differences. RESULTS: Unique to the Th2-high strain, eosinophil: neutrophil ratios in the airways at baseline and following sensitization/aeroallergen challenge were logfold higher in females relative to males, and this was reflected by higher baseline blood eosinophil numbers in females. Pretreatment of Th2-high males with E2 abrogated this sex difference by selectively boosting Th2-associated genes in the airways and eosinophilia, but was without corresponding effect in the Th2-low strain. In contrast, parallel E2 effects on myeloid and lymphoid cell populations were relatively modest. CONCLUSIONS AND CLINICAL RELEVANCE: E2 acts to amplify the eosinophilic component of pre-existing Th2-high immunophenotype, possibly acting at the level of the common eosinophil/neutrophil precursor in bone marrow to preferentially drive eosinophil differentiation. Constitutive granulocyte profiles in which the balance between eosinophils and neutrophils is skewed towards eosinophils have been identified in independent cohort studies as markers of asthma risk, and these findings suggest that more detailed studies on the role of E2 in this context, and in relation to asthma pathogenesis in post-pubertal females in particular, appear warranted.

In infants with sufficient vitamin D status at birth, vitamin D supplementation does not impact immune development.

BACKGROUND: Low vitamin D levels have been associated with allergic diseases. Vitamin D has potent immunomodulatory properties, but the mechanisms remain unclear. We have investigated the effect of oral vitamin D supplementation on circulating immune cell phenotypes in infants. METHOD: A double-blinded randomised controlled trial was conducted to investigate the effect of oral vitamin D supplementation (400 IU/d) on eczema and immune development. A subset of 78 infants was included in this analysis. Phenotypic analysis of immune cell subsets was performed using flow cytometry. RESULTS: Vitamin D supplementation resulted in median 25(OH)D levels of 80.5 vs 59.5 nmol/L in the placebo group at 3 months of age (P = .002) and 87.5 vs 77 nmol/L at 6 months of age (P = .08). We observed significant changes in immune cell composition from birth (cord blood) to 6 months of age. Vitamin D supplementation did not impact these changes, nor did immune cell composition correlate with plasma 25(OH)D levels. Through exploratory analysis, we identified possible associations with eczema development and increased abundance of naïve CD4- T cells at birth, as well as associations with basophils, iNKT and central memory CD4+ T cells, and altered expression patterns of IgE receptor (FcεR1) on monocytes and dendritic cells with eczema at 6 months. CONCLUSIONS: Vitamin D supplementation in infants who were vitamin D sufficient at birth did not affect developmental changes in immune cells during the first 6 months of life. However, immune cell profiles at birth and at 6 months of age were associated with early life eczema.

Progressive increase of FcεRI expression across several PBMC subsets is associated with atopy and atopic asthma within school-aged children.

BACKGROUND: Antigen-specific IgE binds the Fcε receptor I (FcεRI) expressed on several types of immune cells, including dendritic cells (DCs). Activation of FcεRI on DCs in atopics has been shown to modulate immune responses that potentially contribute to asthma development. However, the extent to which DC subsets differ in FcεRI expression between atopic children with or without asthma is currently not clear. This study aimed to analyse the expression of FcεRI on peripheral blood mononuclear cells (PBMCs) from atopic children with and without asthma, and non-atopic/non-asthmatic age-matched healthy controls. METHODS: We performed multiparameter flow cytometry on PBMC from 391 children across three community cohorts and one clinical cohort based in Western Australia. RESULTS: We confirmed expression of FcεRI on basophils, monocytes, plasmacytoid and conventional DCs, with higher proportions of all cell populations expressing FcεRI in atopic compared to non-atopic children. Further, we observed that levels of FcεRI expression were elevated across plasmacytoid and conventional DC as well as basophils in atopic asthmatic compared to atopic non-asthmatic children also after adjusting for serum IgE levels. CONCLUSION: Our data suggest that the expression pattern of FcεRI on DC and basophils differentiates asthmatic from non-asthmatic atopic children. Given the significant immune modulatory effects observed as a consequence of FcεRI expression, this altered expression pattern is likely to contribute to asthma pathology in children.

Functional differences in airway dendritic cells determine susceptibility to IgE-sensitization.

Respiratory IgE-sensitization to innocuous antigens increases the risk for developing diseases such as allergic asthma. Dendritic cells (DC) residing in the airways orchestrate the immune response following antigen exposure and their ability to sample and present antigens to naïve T cells in airway draining lymph nodes contributes to allergen-specific IgE-sensitization. In order to characterize inhaled antigen capture and presentation by DC subtypes in vivo, we used an adjuvant-free respiratory sensitization model using two genetically distinct rat strains, one of which is naturally resistant and the other naturally susceptible to allergic sensitization. Upon multiple exposures to ovalbumin (OVA), the susceptible strain developed OVA-specific IgE and airway inflammation, whereas the resistant strain did not. Using fluorescently tagged OVA and flow cytometry, we demonstrated significant differences in antigen uptake efficiency and presentation associated with either IgE-sensitization or resistance to allergen exposures in respective strains. We further identified CD4+ conventional DC (cDC) as the subset involved in airway antigen sampling in both strains, however, CD4+ cDC in the susceptible strain were less efficient in OVA sampling and displayed increased MHC-II expression compared with the resistant strain. This was associated with generation of an exaggerated Th2 response and a deficiency of airway regulatory T cells in the susceptible strain. These data suggest that subsets of cDC are able to induce either sensitization or resistance to inhaled antigens as determined by genetic background, which may provide an underlying basis for genetically determined susceptibility to respiratory allergic sensitization and IgE production in susceptible individuals.

Immunological Processes Driving IgE Sensitisation and Disease Development in Males and Females.

IgE sensitisation has increased significantly over the last decades and is a crucial factor in the development of allergic diseases. IgE antibodies are produced by B cells through the process of antigen presentation by dendritic cells, subsequent differentiation of CD4⁺ Th2 cells, and class switching in B cells. However, many of the factors regulating these processes remain unclear. These processes affect males and females differently, resulting in a significantly higher prevalence of IgE sensitisation in males compared to females from an early age. Before the onset of puberty, this increased prevalence of IgE sensitisation is also associated with a higher prevalence of clinical symptoms in males; however, after puberty, females experience a surge in the incidence of allergic symptoms. This is particularly apparent in allergic asthma, but also in other allergic diseases such as food and contact allergies. This has been partly attributed to the pro- versus anti-allergic effects of female versus male sex hormones; however, it remains unclear how the expression of sex hormones translates IgE sensitisation into clinical symptoms. In this review, we describe the recent epidemiological findings on IgE sensitisation in male and females and discuss recent mechanistic studies casting further light on how the expression of sex hormones may influence the innate and adaptive immune system at mucosal surfaces and how sex hormones may be involved in translating IgE sensitisation into clinical manifestations.

The complement system in systemic lupus erythematosus: an update.

The complement system plays a major role in the autoimmune disease, systemic lupus erythematosus (SLE). However, the role of complement in SLE is complex since it may both prevent and exacerbate the disease. In this review, we explore the latest findings in complement-focused research in SLE. C1q deficiency is the strongest genetic risk factor for SLE, although such deficiency is very rare. Various recently discovered genetic associations include mutations in the complement receptors 2 and 3 as well as complement inhibitors, the latter related to earlier onset of nephritis. Further, autoantibodies are a distinct feature of SLE that are produced as the result of an adaptive immune response and how complement can affect that response is also being reviewed. SLE generates numerous disease manifestations involving contributions from complement such as glomerulonephritis and the increased risk of thrombosis. Furthermore, since most of the complement system is present in plasma, complement is very accessible and may be suitable as biomarker for diagnosis or monitoring of disease activity. This review highlights the many roles of complement for SLE pathogenesis and how research has progressed during recent years.

Degradation of neutrophil extracellular traps is decreased in patients with antiphospholipid syndrome.

OBJECTIVES: A decreased ability to degrade neutrophil extracellular traps (NETs) is seen in a subgroup of patients with systemic lupus erythematosus (SLE) and correlates with the presence of autoantibodies. Antiphospholipid syndrome (APS) can develop secondary to SLE or as a primary disease. In the current study we investigated the ability of sera from patients with APS to degrade NETs. The presence of antibodies against NETs and neutrophil remnants were also determined in the same patients. METHODS: In the study, 106 patients with APS (73 primary and 33 secondary), 76 patients with systemic sclerosis (SSc) and 77 healthy donors as control samples were included. NETs generated from neutrophils isolated from healthy volunteers were incubated with patient sera, followed by measurement of degraded NETs or deposited IgG. RESULTS: Sera of APS patients had a decreased ability to degrade NETs compared to healthy controls, with no difference between primary and secondary APS. Sera from SSc patients did not differ significantly from healthy controls in the ability to degrade NETs. A decreased degradation of NETs correlated weakly to increased levels of antibodies against NETs/neutrophil remnants in patients with primary APS, but stronger in patients with secondary APS. CONCLUSIONS: The ability to degrade NETs is decreased in a subgroup of patients with APS and is associated with antibodies against NETs and specific clinical manifestations in those patients.

Neutrophil extracellular traps that are not degraded in systemic lupus erythematosus activate complement exacerbating the disease.

Ongoing inflammation including activation of the complement system is a hallmark of systemic lupus erythematosus (SLE). Antimicrobial neutrophil extracellular traps (NETs) are composed of secreted chromatin that may act as a source of autoantigens typical for SLE. In this study, we investigated how complement interacts with NETs and how NET degradation is affected by complement in SLE patients. We found that sera from a subset of patients with active SLE had a reduced ability to degrade in vitro-generated NETs, which was mostly restored when these patients were in remission. Patients that failed to degrade NETs had a more active disease and they also displayed lower levels of complement proteins C4 and C3 in blood. We discovered that NETs activated complement in vitro and that deposited C1q inhibited NET degradation including a direct inhibition of DNase-I by C1q. Complement deposition on NETs may facilitate autoantibody production, and indeed, Abs against NETs and NET epitopes were more pronounced in patients with impaired ability to degrade NETs. NET-bound autoantibodies inhibited degradation but also further increased C1q deposition, potentially exacerbating the disease. Thus, NETs are a potent complement activator, and this interaction may play an important role in SLE. Targeting complement with inhibitors or by removing complement activators such as NETs could be beneficial for patients with SLE.

Annexin A2 and A5 serve as new ligands for C1q on apoptotic cells.

C1q is the initiator of the classical complement pathway and opsonizes apoptotic cells to facilitate phagocytosis. Deficiency of C1q is the strongest known risk factor for development of systemic lupus erythematosus (SLE), which appears to be related to ensuing impaired clearance of apoptotic material. The objective of the current study was to investigate new ligands for C1q on the surface of apoptotic cells. We revealed that the two phospholipid-binding proteins annexin A2 and A5 are, beside DNA, significant C1q ligands. We furthermore, demonstrated that C1q binds directly to histones exposed on the surface of dying cells but we did not detect significant interaction with phosphatidylserine. The complement inhibitors C4b-binding protein and factor H also interact with dying cells, most likely to decrease complement activation beyond the level of C3 to allow noninflammatory clearance. Despite the fact that C4b-binding protein, factor H, and C1q share some ligands on dying cells, we showed that these three proteins did not compete with one another for binding to apoptotic cells. We additionally demonstrated that the way in which apoptosis is induced influenced both the degree of apoptosis and the binding of C1q. The knowledge, that annexin A2 and A5 act as ligands for C1q on apoptotic cells, sheds new light on the pathophysiology of autoimmune diseases.

Sex-Specific Environmental Impacts on Initiation and Progression of Multiple Sclerosis.

The immunological mechanisms that contribute to multiple sclerosis (MS) differ between males and females. Females are 2-3 times more likely to develop MS compared to males, however the reason for this discrepancy is unknown. Once MS is established, there is a more inflammatory yet milder form of disease in females whereas males generally suffer from more severe disease and faster progression, neural degradation, and disability. Some of these differences relate to genetics, including genetic control of immune regulatory genes on the X-chromosome, as well as immune modulatory properties of sex hormones. Differences in MS development may also relate to how sex interacts with environmental risk factors. There are several environmental risk factors for MS including late-onset Epstein Barr virus infection, low serum vitamin D levels, low UV radiation exposure, smoking, obesity, and lack of physical activity. Most of these risk factors impact males and females differently, either due to biological or immunological processes or through behavioral differences. In this review, we explore these differences further and focus on how the interaction of environmental risk factors with sex hormones may contribute to significantly different prevalence and pathology of MS in males and females.

Epstein-Barr virus infection, B-cell dysfunction and other risk factors converge in gut-associated lymphoid tissue to drive the immunopathogenesis of multiple sclerosis: a hypothesis.

Multiple sclerosis is associated with Epstein-Barr virus (EBV) infection, B-cell dysfunction, gut dysbiosis, and environmental and genetic risk factors, including female sex. A disease model incorporating all these factors remains elusive. Here, we hypothesise that EBV-infected memory B cells (MBCs) migrate to gut-associated lymphoid tissue (GALT) through EBV-induced expression of LPAM-1, where they are subsequently activated by gut microbes and/or their products resulting in EBV reactivation and compartmentalised anti-EBV immune responses. These responses involve marginal zone (MZ) B cells that activate CD4+ T-cell responses, via HLA-DRB1, which promote downstream B-cell differentiation towards CD11c+/T-bet+ MBCs, as well as conventional MBCs. Intrinsic expression of low-affinity B-cell receptors (BCRs) by MZ B cells and CD11c+/T-bet+ MBCs promotes polyreactive BCR/antibody responses against EBV proteins (e.g. EBNA-1) that cross-react with central nervous system (CNS) autoantigens (e.g. GlialCAM). EBV protein/autoantigen-specific CD11c+/T-bet+ MBCs migrate to the meningeal immune system and CNS, facilitated by their expression of CXCR3, and induce cytotoxic CD8+ T-cell responses against CNS autoantigens amplified by BAFF, released from EBV-infected MBCs. An increased abundance of circulating IgA+ MBCs, observed in MS patients, might also reflect GALT-derived immune responses, including disease-enhancing IgA antibody responses against EBV and gut microbiota-specific regulatory IgA+ plasma cells. Female sex increases MZ B-cell and CD11c+/T-bet+ MBC activity while environmental risk factors affect gut dysbiosis. Thus, EBV infection, B-cell dysfunction and other risk factors converge in GALT to generate aberrant B-cell responses that drive pathogenic T-cell responses in the CNS.

Potential immunological effects of gender-affirming hormone therapy in transgender people - an unexplored area of research.

There are well-described sex-based differences in how the immune system operates. In particular, cisgender (cis) females have a more easily activated immune system; associated with an increased prevalence of autoimmune diseases and adverse events following vaccinations. Conversely, cis males have a higher threshold for immune activation, and are more prone to certain infectious diseases, such as coronavirus disease (COVID-19). Oestrogen and testosterone have immune-modulatory properties, and it is likely that these contribute to the sexual dimorphism of the immune system. There are also important immune-related genes located on the X chromosome, such as toll-like receptor (TLR) 7/8; and the mosaic bi-allelic expression of such genes may contribute to the state of immune hyperactivation in cis females. The scientific literature strongly suggests that sex-based differences in the functioning of the immune system are related to both X-linked genes and immune modulation by sex hormones. However, it is currently not clear how this impacts transgender (trans) people receiving gender-affirming hormonal therapy. Moreover, it is estimated that in Australia, at least 2.3% of adolescents identify as trans and/or gender diverse, and referrals to specialist gender-affirming care are increasing each year. Despite the improving social awareness of trans people, they remain chronically underrepresented in the scientific literature. In addition, a small number of case studies describe new onset autoimmune disorders in adult trans females following oestrogen use. However, there is currently minimal long-term research with an immunological focus on trans people. Therefore, to ensure the positive health outcomes of trans people, it is crucial that the role of sex hormones in immune modulation is investigated further.

Circulating Memory B Cells in Early Multiple Sclerosis Exhibit Increased IgA+ Cells, Globally Decreased BAFF-R Expression and an EBV-Related IgM+ Cell Signature.

Multiple sclerosis (MS) is an immune-mediated inflammatory disease of the central nervous system that results in demyelination of axons, inefficient signal transmission and reduced muscular mobility. Recent findings suggest that B cells play a significant role in disease development and pathology. To further explore this, B cell profiles in peripheral blood from 28 treatment-naive patients with early MS were assessed using flow cytometry and compared to 17 healthy controls. Conventional and algorithm-based analysis revealed a significant increase in MS patients of IgA+ memory B cells (MBC) including CD27+, CD27- and Tbet+ subsets. Screening circulating B cells for markers associated with B cell function revealed a significantly decreased expression of the B cell activation factor receptor (BAFF-R) in MS patients compared to controls. In healthy controls, BAFF-R expression was inversely associated with abundance of differentiated MBC but this was not observed in MS. Instead in MS patients, decreased BAFF-R expression correlated with increased production of proinflammatory TNF following B cell stimulation. Finally, we demonstrated that reactivation of Epstein Barr Virus (EBV) in MS patients was associated with several phenotypic changes amongst MBCs, particularly increased expression of HLA-DR molecules and markers of a T-bet+ differentiation pathway in IgM+ MBCs. Together, these data suggest that the B cell compartment is dysregulated in MS regarding aberrant MBC homeostasis, driven by reduced BAFF-R expression and EBV reactivation. This study adds further insights into the contribution of B cells to the pathological mechanisms of MS, as well as the complex role of BAFF/BAFF-R signalling in MS.

Annexin-II, DNA, and histones serve as factor H ligands on the surface of apoptotic cells.

Apoptotic cells are opsonized by complement components such as C1q and C3b, which increases their susceptibility to phagocytosis. Soluble complement inhibitors such as factor H (fH) also recognize apoptotic cells to minimize the pro-inflammatory effects of downstream complement activation. We used four radiolabeled protein constructs that span different regions of the 20 complement control protein (CCP) modules that make up fH and found that fragments comprising CCPs 6-8, CCPs 8-15, and CCPs 19-20 but not CCPs 1-4, bound to apoptotic Jurkat T cells. There are four possible ligand types on apoptotic cells that could recruit fH: proteins, carbohydrates, lipids, and DNA. We found that CCPs 6-8 of fH bind to annexin-II, a trypsin-insensitive protein that becomes exposed on surfaces of apoptotic cells. The second ligand of fH, which interacts with CCPs 6-8 and 19-20, is DNA. Confocal microscopy showed co-localization of fH with antibodies specific for DNA. fH also binds to histones devoid of DNA, and CCPs 1-4, 6-8, and 8-15 mediate this interaction. Treatment of apoptotic cells with neuraminidase, chondroitinase, heparitinase, and heparinase did not change fH binding. Treatment of apoptotic cells with phospholipase A(2) dramatically increased both binding of fH and cell-surface DNA. We also excluded the possibility that fH interacts with lysophospholipids using surface plasmon resonance and flow cytometry with lipid-coated beads. Identification of annexin-II as one of the fH ligands on apoptotic cells together with the fact that autoantibodies against annexin-II are found in systemic lupus erythematosus provides further insight into understanding the pathogenesis of this disease.

Associations of serum short-chain fatty acids with circulating immune cells and serum biomarkers in patients with multiple sclerosis.

Altered composition of gut bacteria and changes to the production of their bioactive metabolites, the short-chain fatty acids (SCFAs), have been implicated in the development of multiple sclerosis (MS). However, the immunomodulatory actions of SCFAs and intermediaries in their ability to influence MS pathogenesis are uncertain. In this study, levels of serum SCFAs were correlated with immune cell abundance and phenotype as well as with other relevant serum factors in blood samples taken at first presentation of Clinically Isolated Syndrome (CIS; an early form of MS) or MS and compared to healthy controls. There was a small but significant reduction in propionate levels in the serum of patients with CIS or MS compared with healthy controls. The frequencies of circulating T follicular regulatory cells and T follicular helper cells were significantly positively correlated with serum levels of propionate. Levels of butyrate associated positively with frequencies of IL-10-producing B-cells and negatively with frequencies of class-switched memory B-cells. TNF production by polyclonally-activated B-cells correlated negatively with acetate levels. Levels of serum SCFAs associated with changes in circulating immune cells and biomarkers implicated in the development of MS.

IRF7-Associated Immunophenotypes Have Dichotomous Responses to Virus/Allergen Coexposure and OM-85-Induced Reprogramming.

High risk for virus-induced asthma exacerbations in children is associated with an IRF7lo immunophenotype, but the underlying mechanisms are unclear. Here, we applied a Systems Biology approach to an animal model comprising rat strains manifesting high (BN) versus low susceptibility (PVG) to experimental asthma, induced by virus/allergen coexposure, to elucidate the mechanism(s)-of-action of the high-risk asthma immunophenotype. We also investigated potential risk mitigation via pretreatment with the immune training agent OM-85. Virus/allergen coexposure in low-risk PVG rats resulted in rapid and transient airways inflammation alongside IRF7 gene network formation. In contrast, responses in high-risk BN rats were characterized by severe airways eosinophilia and exaggerated proinflammatory responses that failed to resolve, and complete absence of IRF7 gene networks. OM-85 had more profound effects in high-risk BN rats, inducing immune-related gene expression changes in lung at baseline and reducing exaggerated airway inflammatory responses to virus/allergen coexposure. In low-risk PVG rats, OM-85 boosted IRF7 gene networks in the lung but did not alter baseline gene expression or cellular influx. Distinct IRF7-associated asthma risk immunophenotypes have dichotomous responses to virus/allergen coexposure and respond differentially to OM-85 pretreatment. Extrapolating to humans, our findings suggest that the beneficial effects OM-85 pretreatment may preferentially target those in high-risk subgroups.