Generation of gut-homing IgA-secreting B cells by intestinal dendritic cells

New thoughts on the intestinal microbiome-B cell-IgA axis and therapies in IgA nephropathy

IgA nephropathy (IgAN), as the most common chronic glomerulonephritis worldwide, is often triggered by mucosal infections and follows a chronic progression, with the majority of patients ultimately progressing to end-stage renal disease (ESRD) during their lifetimes. Since the mystery of its complete pathogenesis has not been fully solved, the resulting lack of effective early diagnosis and treatment greatly affects the prognosis of patients. Given the well-defined pathological feature of IgA deposition in the mesangial region, the source and role of pathogenic IgA has been focused on. Starting from the microbiology and immunity of the gut, we systematically review both the physiological and the pathological process of microbiome-B cell-IgA axis, from microbial-induced IgA production to the role of IgA in the intestinal immune milieu, and ultimately end up with the various aspects of microbiome-B cell-IgA axis in the pathogenesis of IgAN as well as the corresponding therapeutic initiatives available. Our retrospective review helps researchers to systematically understand the complex role between intestinal flora dysbiosis and pathogenic IgA in IgAN. This understanding provides a foundation for in-depth explorations to uncover more detailed pathogenic mechanisms and to develop more precise and effective diagnostic and therapeutic approaches.

Clostridium butyricum-induced balance in colonic retinol metabolism and short-chain fatty acid levels inhibit IgA-related mucosal immunity and relieve colitis developments

Gut microbiota and their metabolites play a significant role in inflammatory bowel disease. Here, we attempted to determine the anti-inflammatory role of the probiotic Clostridium. butyricum (CB) in inflammatory bowel disease and identify the exact immune mechanism. The clinical significance of Clostridiales and CB was explored in patients with ulcerative colitis. The inflammation-suppressive role of CB was evaluated in mice with DSS-induced colitis. 16S rRNA sequencing was performed to assess changes in the gut microbiota. Altered transcription levels were detected by RNA sequencing. Flow cytometry was performed to assess the frequency of IgA responses to gut microbiota. Clostridiales and CB were depleted in ulcerative colitis. Oral gavage with CB significantly suppressed weight loss and colon shortening in the dextran sulfate sodium-induced colitis mouse model. Intestinal barrier injury was reversed and the gut microbiota was restored upon treatment with CB administration. The mucosal immune response to gut microbiota was reversed upon treatment with CB. CB conditional medium was more effective than heat-killed CB in alleviating inflammation. Mechanistically, retinol metabolism and retinoic acid levels were higher in groups treated with CB and butyrate. CB and the metabolite butyrate exerted a suppressive role on the abundance of Immunoglobulin A-coated gut microbiota by inhibiting retinoic acid synthesis. In summary, CB protects against inflammation and intestinal barrier injury by producing anti-inflammatory metabolites that can regulate the mucosal immune response to gut microbiota by increasing retinoic acid levels in the colon.

The influence of the gut microbiota on B cells in autoimmune diseases

Mounting evidence shows that gut microbiota communities and the human immune system coexist and influence each other, and there are a number of reports of a correlation between specific changes in gut microbiota and the occurrence of autoimmune diseases. B lymphocytes play a central role in the regulation of both gut microbiota communities and in autoimmune diseases. Here, we summarize evidence of the influence of gut microbiota-B cell pathways on autoimmune diseases and how B cells regulate microorganisms, which provides mechanistic insights with relevance for identification of potential therapeutic targets and related fields.

Donor human milk pasteurization methods and the effect on milk components as they relate to Necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an intestinal disease that predominantly occurs in preterm infants. While there are no definitive treatment options for NEC, the administration of human milk is protective against the development of NEC in preterm infants. However, human milk composition is highly dynamic, containing numerous bioactive components that can be affected by both maternal and perinatal factors. Furthermore, when maternal milk is unavailable, donor human milk, which goes through a rigorous preparation process including pooling and pasteurization, is used. The different pasteurization methods can have implications for the bioactive components of human milk. In this review, we explore the current literature surrounding the benefits of human milk in the prevention of NEC. We further review the bioactive components and the microbiome of human milk and the many factors that affect the diversity of milk content between human milk samples. Finally, we review the different methods of pasteurization and their effects on the components of human milk.

Immunostimulatory effects of Heyndrickxia coagulans SANK70258

Here, we examined the immunomodulating effects of Heyndrickxia coagulans SANK70258 (SANK70258). Mouse splenocytes treated with γ-ray-irradiated SANK70258 produced higher levels of interferon (IFN)-γ than those with 7 types of lactic acid bacteria. IFN-γ was mainly produced by natural killer (NK) cells, involving IL-12/IL-23, dendritic cells (DCs), and NF-κB signaling. SANK70258 induced the release of IL-6, IL-10, and IL-12p40 from mouse DCs and the expression of cytokine genes in the human monocyte. Cytokine release from SANK70258-treated DCs was partially reduced by the knockdown of Tlr2 or Nod2, and was abolished by Myd88 knockout. DC-stimulating components of SANK70258 were enriched in ether- and butanol-insoluble peptidoglycan-related fractions. The SANK70258 component induced high levels of immunoglobulin (Ig) A production in Peyer's patch cells, and its oral intake significantly increased intestinal IgA and IgA-expressing B cells in Peyer's patches in mice. We conclude that the SANK70258 component exhibits high activity as an immunostimulant that induces the production of IFN-γ and IgA.

Biomarker expression level changes within rectal gut-associated lymphoid tissues in spinal cord-injured rats

Neurogenic bowel dysfunction (NBD) is common after spinal cord injury (SCI). Gut-associated lymphoid tissue (GALT), an organized structure within the mucosal immune system, is important for the maintenance of gut homeostasis and body health and serves as the first line barrier/defense against diet antigens, commensal microbiota, pathogens, and toxins in mucosal areas. The current study examined gene expression levels along six segments of anorectal tissue using real-time polymerase chain reaction (RT-PCR) in uninjured rats (28-day sham surgical controls) and at both 28- and 42-days post-T9 contusion injury. Consistent with our previous report of functional regional differences in the ano-rectum, we demonstrate the existence of GALTs located primarily within the segment at 3-4.5 cm from the rectal dentate line (termed rectal GALTs-rGALTs) in shams with upregulated gene expression levels of multiple biomarkers, including B cell and T cell-related genes, major histocompatibility complex (MHC) class II molecules, and germinal center (GC)-related genes, which was further confirmed by histologic examination. In the same rectal tissue segment following T9 SCI, inflammation-related genes were upregulated at 28 days post-injury (DPI) indicating that microbial infection and inflammation of rGALTs modified structure and function of rGALTs, while at 42 DPI rGALTs exhibited resolution of inflammation and impaired structure/function for extrafollicular B cell responses. Taken together, our data suggest that rGALTs exists in rat rectum for homeostasis of gut microbiota/barrier. SCI induces microbial infection and inflammation in rectal tissues containing rGALTs, which could contribute to development of SCI-related gut microbiome dysbiosis, NBD, and systemic diseases.

Immune-endocrine crossroads: the impact of nuclear receptors in Tuberculosis and Chagas disease

Nuclear Receptors (NRs) comprise a superfamily of proteins with essential roles in cell signaling, survival, proliferation, and metabolism. They act as transcription factors and are subclassified into families based on their ligands, DNA-binding sequences, tissue specificity, and functions. Evidence indicates that in infectious diseases, cancer, and autoimmunity, NRs modulate immune and endocrine responses, altering the transcriptional profile of cells and organs and influencing disease progression. Chronic infectious diseases, characterized by pathogen persistence, are particularly notable for an exaggerated inflammatory process. Unlike acute inflammation, which helps the host respond to pathogens, chronic inflammation leads to metabolic disorders and a dysregulated neuro-immuno-endocrine response. Over time, disturbances in cytokine, hormone, and other compound production foster an unbalanced, detrimental defensive response. This complexity underscores the significant role of ligand-dependent NRs. Tuberculosis and Chagas Disease are two critical chronic infections. The causative agents, Mycobacterium tuberculosis and Trypanosoma cruzi, have developed evasion strategies to establish chronic infections. Their clinical manifestations are associated with disrupted immuno-endocrine responses, pointing to a potential involvement of NRs. This review explores the current understanding of NRs in regulating immune-endocrine interactions within the context Tuberculosis and Chagas Disease. These diseases remain significant global health concerns, particularly in developing countries, highlighting the importance of understanding the molecular mechanisms underlying host-pathogen interactions mediated by NRs.

Retinoic acid-adjuvanted vaccine induces antigen-specific secretory IgA in the gut of newborn piglets

Mucosal secretory IgA (SIgA) produced by subepithelial plasma cells in the lamina propria is the major antigen-specific defense mechanism against mucosal infections. We investigated if a retinoic acid (RA)-containing adjuvant in parenteral immunization, can induce vaccine-specific SIgA in the jejunal lumen in a dose-dependent manner in neonatal pigs immunized with a Chlamydia hybrid antigen. To accurately quantify SIgA responses in mucosal secretions, an antigen-specific ELISA method with secondary detection of porcine secretory component rather than IgA was developed. RA facilitated a stronger (or faster) IgG, IgA, IgM and SIgA response in serum after primary immunization, and a more than 10-fold significantly increased level of vaccine-specific SIgA in jejunum at termination 2 weeks after the secondary boost, whereas IgA or SIgA responses in bronchoalveolar lavage (BAL) were not significantly increased after immunization with RA. Analyses of different isotype responses to vaccination and different sampling sites, revealed significant correlations between IgG and IgA responses in serum, and between IgG in serum and jejunum, while IgA in jejunum was neither correlated with IgA in serum nor with IgG in jejunum. This is indicative of IgG in jejunum being primarily a transudate from serum, while IgA is not. Jejunum SIgA correlated significantly with jejunum IgA and with both serum SIgA and IgA. Our results thus support the use of SC-specific reagents for mucosal SIgA responses, although IgA reagents to a lesser extent also reflects local antibodies. Although the IgA and SIgA levels in BAL were not significantly different with or without RA, we observed a significant correlation of vaccine-specific SIgA in jejunum and BAL, indicating a level of commonality in the regulation of mucosal antibodies in gut and respiratory system. In conclusion, an adjuvant with high concentration of RA was shown to increase the local intestinal mucosal antibody response after parenteral immunization in pigs.

Proportions of IgA antibodies targeting glycosylated epitopes of secreted Escherichia coli mucinase YghJ in initial plasmablast response differ from salivary and intestinally secreted IgA

Mucosal infections normally cause an immune response including activation of antigen-specific B cells in regional mucosa-associated lymphoid tissue. After recirculation of plasmablasts, and maturation at mucosal surfaces or bone marrow, plasma cells produce secretory or systemic IgA. It remains uncertain to what extent secretory and systemic IgA share the same target specificities. For vaccine candidate optimization, it is important to know whether IgA targeting of glycosylated epitopes of a protein antigen vary between mucosal and systemic sites. We evaluated glycosylated epitope specificity of systemic and mucosally secreted IgA against YghJ, a potential vaccine candidate antigen secreted by most pathogenic Escherichia coli. IgA from intestinal lavage, saliva, serum, and blood-derived antibody in lymphocyte supernatants (ALS) were collected from 21 volunteers following experimental infection with enterotoxigenic E. coli. Methods for preparing IgA from saliva and ALS were developed, and multiplex bead flow cytometric immunoassays were used to determine levels of IgA targeting natively glycosylated YghJ and estimating what proportion of these antibodies specifically targeted glycosylated epitopes. Following infection, anti-YghJ IgA levels increased substantially for most volunteers across all four specimen types. Target specificity of ALS IgA correlated well with serum IgA, but not with mucosally secreted IgA. Furthermore, glycosylation-specific proportion of salivary IgA was higher than, and did not correlate with, intestinally secreted IgA. These results indicate a new degree of complexity to our understanding of epitope-targeting and tissue specificity of mucosal antibody responses. Our findings also suggest that all features of an intestinal IgA response may not be well reflected in serum, saliva, or ALS, which are commonly used proxy specimens for evaluating intestinal immune responses.

A pan-family screen of nuclear receptors in immunocytes reveals ligand-dependent inflammasome control

Ligand-dependent transcription factors of the nuclear receptor (NR) family regulate diverse aspects of metazoan biology, enabling communications between distant organs via small lipophilic molecules. Here, we examined the impact of each of 35 NRs on differentiation and homeostatic maintenance of all major immunological cell types in vivo through a "Rainbow-CRISPR" screen. Receptors for retinoic acid exerted the most frequent cell-specific roles. NR requirements varied for resident macrophages of different tissues. Deletion of either Rxra or Rarg reduced frequencies of GATA6+ large peritoneal macrophages (LPMs). Retinoid X receptor alpha (RXRα) functioned conventionally by orchestrating LPM differentiation through chromatin and transcriptional regulation, whereas retinoic acid receptor gamma (RARγ) controlled LPM survival by regulating pyroptosis via association with the inflammasome adaptor ASC. RARγ antagonists activated caspases, and RARγ agonists inhibited cell death induced by several inflammasome activators. Our findings provide a broad view of NR function in the immune system and reveal a noncanonical role for a retinoid receptor in modulating inflammasome pathways.

Amelioration of immunoglobulin A vasculitis by suppression of the pathological expansion of T follicular helper 17 cells

The main pathogenic features of immunoglobulin A vasculitis (IgAV) are overactive B cells and elevated production of IgA, which requires help from T follicular helper 17 (Tfh17) cells. To evaluate the pathological role of Tfh17 cells in IgAV, we investigated the mechanism responsible for Tfh17 differentiation and explored how to ameliorate IgAV by modulating Tfh17 generation. Peripheral blood mononuclear cells from IgAV patients were analyzed by flow cytometry. In vitro culture was performed to assess the modulation of cytokine-induced phenotypes. IgAV rats were used to explore the therapeutic effects of IL-6 blockade and the regulatory functions of IL-6 in Tfh17 cells. Serum cytokine and IgA levels were measured by ELISA while histopathological changes were evaluated by H&E,PAS or immunofluorescence staining. Frequency of CD4+CXCR5+CCR6+ Tfh17 cells were increased in IgAV patients and associated with disease severity. There was also a significant infiltration of Tfh17 cells in the kidney of human IgAV nephritis patients. IL-6 promoted the dendritic cell production of TGF-β and Tfh17 differentiation. In IgAV rats, the in vivo blockade of IL-6 signaling inhibited Tfh17 differentiation, resulting in reduction of the germinal center and IgA production. Suppression of Tfh17 cells using IL-6 blockade greatly ameliorated clinical symptoms such as hemorrhagic rash and bloody stool and decreased IgA deposition and mesangial proliferation in the kidney in IgAV rats. Our findings suggest that suppression of Tfh17 differentiation can alleviate IgA-mediated vasculitis and may permit the development of tailored medicines for treating IgAV.

Immunoglobulin A Antibodies: From Protection to Harmful Roles

Immunoglobulin A (IgA) is the most abundantly produced antibody in humans. IgA is a unique class of immunoglobulin due to its multiple molecular forms, and a defining difference between the two subclasses: IgA1 has a long hinge-region that is heavily O-glycosylated, whereas the IgA2 hinge-region is shorter but resistant to bacterial proteases prevalent at mucosal sites. IgA is essential for immune homeostasis and education. Mucosal IgA plays a crucial role in maintaining the integrity of the mucosal barrier by immune exclusion of pathobionts while facilitating colonization with certain commensals; a large part of the gut microbiota is coated with IgA. In the circulation, monomeric IgA that has not been engaged by antigen plays a discrete role in dampening inflammatory responses. Protective and harmful roles of IgA have been studied over several decades, but a new understanding of the complex role of this immunoglobulin in health and disease has been provided by recent studies. Here, we discuss the physiological and pathological roles of IgA with a special focus on the gut, kidneys, and autoimmunity. We also discuss new IgA-based therapeutic approaches.

Cholesterol sensing and metabolic adaptation in tissue immunity

Cholesterol metabolites, particularly oxidized forms known as oxysterols, play crucial roles in modulating immune and metabolic processes across various tissues. Concentrations of local cholesterol and its metabolites influence tissue-specific immune responses by shaping the metabolic and spatial organization of immune cells in barrier organs like the small intestine (SI) and lungs. We explore recent molecular and cellular evidence supporting the metabolic adaptation of innate and adaptive immune cells in the SI and lung, driven by cholesterol and cholesterol metabolites. Further research should unravel the detailed molecular mechanisms and spatiotemporal adaptations involving cholesterol metabolites in distinct mucosal tissues in homeostasis or infection. We posit that pharmacological interventions targeting the generation or sensing of cholesterol metabolites might be leveraged to enhance long-term immune protection in mucosal tissues or prevent autoinflammatory states.

Mouse enteric neurons control intestinal plasmacytoid dendritic cell function via serotonin-HTR7 signaling

Serotonergic neurons in the central nervous system control behavior and mood, but knowledge of the roles of serotonergic circuits in the regulation of immune homeostasis is limited. Here, we employ mouse genetics to investigate the functions of enteric serotonergic neurons in the control of immune responses and find that these circuits regulate IgA induction and boost host defense against oral, but not systemic Salmonella Typhimurium infection. Enteric serotonergic neurons promote gut-homing, retention and activation of intestinal plasmacytoid dendritic cells (pDC). Mechanistically, this neuro-immune crosstalk is achieved through a serotonin-5-HT receptor 7 (HTR7) signaling axis that ultimately facilitates the pDC-mediated differentiation of IgA+ B cells from IgD+ precursors in the gut. Single-cell RNA-seq data further reveal novel patterns of bidirectional communication between specific subsets of enteric neurons and lamina propria DC. Our findings thus reveal a close interplay between enteric serotonergic neurons and gut immune homeostasis that enhances mucosal defense.

Oral reovirus reshapes the gut microbiome and enhances antitumor immunity in colon cancer

The route of oncolytic virotherapy is pivotal for immunotherapeutic efficacy in advanced cancers. In this preclinical study, an oncolytic reovirus (RC402) is orally administered to induce antitumor immunity. Oral reovirus treatment shows no gross toxicities and effectively suppresses multifocal tumor lesions. Orally administered reovirus interacts with the host immune system in the Peyer's patch of the terminal ileum, increases IgA+ antibody-secreting cells in the lamina propria through MAdCAM-1+ blood vessels, and reshapes the gut microbiome. Oral reovirus promotes antigen presentation, type I/II interferons, and T cell activation within distant tumors, but does not reach or directly infect tumor cells beyond the gastrointestinal tract. In contrast to intratumoral reovirus injection, the presence of the gut microbiome, Batf3+ dendritic cells, type I interferons, and CD8+ T cells are indispensable for orally administered reovirus-induced antitumor immunity. Oral reovirus treatment is most effective when combined with αPD-1(L1) and/or αCTLA-4, leading to complete colon tumor regression and protective immune memory. Collectively, oral reovirus virotherapy is a feasible and effective immunotherapeutic strategy in preclinical studies.

Retinoic Acid (RA): A Critical Immunoregulatory Molecule in Asthma and Allergies

INTRODUCTION

Asthma and allergies are chronic inflammatory disorders that are triggered owing to aberrant responses of the immune system against typically innocent environmental substances. Retinoic acid (RA) represents a biologically active metabolite of vitamin A (VA) and high-affinity ligand for RA receptor (RAR) that is implicated in a wide variety of biological processes, including cell proliferation, differentiation, apoptosis, organogenesis, reproduction, and immune responses. In the immune system, RA contributes to the induction of regulatory T (Treg) cells, adhesion molecules required for homing of B and T cells in the gut, and tolerance. Noteworthy, RA has a pivotal role in maintaining the balance of Th17-Treg cells and is also indispensable for appropriate responses of T helper (Th) cells.

AIMS

This mini-review article intends to expose the immune functions of RA, with an emphasis on the enzymatic pathways converting VA into RA and its receptor-dependent actions in asthma and allergies.

CONCLUSIONS

Recent findings have depicted that RA levels are reduced in asthma and allergies and that treatment with RA alleviates allergy symptoms and airway inflammation. RA also modulates allergic airway disorders by inhibiting Th2/Th17 response and increasing Treg cells. Therefore, RA could be considered a novel and promising therapeutic agent to be studied and used for treating these diseases.

Human intestinal stromal cells promote homeostasis in normal mucosa but inflammation in Crohn's disease in a retinoic acid-deficient manner

Intestinal stromal cells (SCs), which synthesize the extracellular matrix that gives the mucosa its structure, are newly appreciated to play a role in mucosal inflammation. Here, we show that human intestinal vimentin+CD90+smooth muscle actin- SCs synthesize retinoic acid (RA) at levels equivalent to intestinal epithelial cells, a function in the human intestine previously attributed exclusively to epithelial cells. Crohn's disease SCs (Crohn's SCs), however, synthesized markedly less RA than SCs from healthy intestine (normal SCs). We also show that microbe-stimulated Crohn's SCs, which are more inflammatory than stimulated normal SCs, induced less RA-regulated differentiation of mucosal dendritic cells (DCs) (circulating pre-DCs and monocyte-derived DCs), leading to the generation of more potent inflammatory interferon-γhi/interleukin-17hi T cells than normal SCs. Explaining these results, Crohn's SCs expressed more DHRS3, a retinaldehyde reductase that inhibits retinol conversion to retinal and, thus, synthesized less RA than normal SCs. These findings uncover a microbe-SC-DC crosstalk in which luminal microbes induce Crohn's disease SCs to initiate and perpetuate inflammation through impaired synthesis of RA.

CXCR4-enriched T regulatory cells preferentially home to bone marrow and resolve inflammation

CXCR4 cell surface expression is critical for the homing of T regulatory (Treg) cells to the bone marrow (BM). We hypothesize that CXCR4 enrichment on Tregs cell surface may abbreviate their transit time to reach BM. Umbilical cord-blood CD25+ Tregs underwent CXCR4 dual enrichment and ex vivo expansion using the CRANE process to generate CXCR4-enriched Tregs (TregCXCR4) cells, which showed a faster migration across the Transwell membrane toward CXCL12/stromal cell-derived factor 1α (SDF1α) at 15, 30, and 60 min, when compared to unmanipulated Tregcontrol cells (p < 0.0001). TregCXCR4 exhibited preferential homing to BM in vivo at 12 and 24 h. Metacluster analysis of BM showed a decrease in CD8+ and an increase in CD39 and CD73 and CXCR5 when compared to Tregcontrol. TregCXCR4 decreased plasma TGF-β1/β2 and IFN-γ levels. When compared to control, TregCXCR4 cells decreased in CD8+ T cell, IFN-γ, and TNF-α expression in BM. We conclude that TregCXCR4 show enhanced migration toward CXCL12/SDF1α and a preferential homing to BM resulting in resolution of inflammation.

Role of cellular effectors in the induction and maintenance of IgA responses leading to protective immunity against enteric bacterial pathogens

The mucosal immune system is a critical first line of defense to infectious diseases, as many pathogens enter the body through mucosal surfaces, disrupting the balanced interactions between mucosal cells, secretory molecules, and microbiota in this challenging microenvironment. The mucosal immune system comprises of a complex and integrated network that includes the gut-associated lymphoid tissues (GALT). One of its primary responses to microbes is the secretion of IgA, whose role in the mucosa is vital for preventing pathogen colonization, invasion and spread. The mechanisms involved in these key responses include neutralization of pathogens, immune exclusion, immune modulation, and cross-protection. The generation and maintenance of high affinity IgA responses require a delicate balance of multiple components, including B and T cell interactions, innate cells, the cytokine milieu (e.g., IL-21, IL-10, TGF-β), and other factors essential for intestinal homeostasis, including the gut microbiota. In this review, we will discuss the main cellular components (e.g., T cells, innate lymphoid cells, dendritic cells) in the gut microenvironment as mediators of important effector responses and as critical players in supporting B cells in eliciting and maintaining IgA production, particularly in the context of enteric infections and vaccination in humans. Understanding the mechanisms of humoral and cellular components in protection could guide and accelerate the development of more effective mucosal vaccines and therapeutic interventions to efficiently combat mucosal infections.

The Role of Mucosal Immunity: What Can We Learn From Animal and Human Studies?

Immunoglobulin A (IgA) is a key actor in the mucosal immune system, which moderates interactions between the host and environmental factors such as food antigens and commensal microorganisms. The pathogenesis of IgA nephropathy (IgAN) involves a multistep process starting with deglycosylation of mucosally derived, polymeric IgA1 (dg-IgA1) that reaches the circulation. Modified O-glycans on dg-IgA1 are targeted by IgG-autoantibodies, leading to the formation of circulating immune complexes that deposit in the glomerular mesangium. Infections of mucosal surfaces trigger flares of primary IgAN, while inflammatory bowel disease and liver cirrhosis are important causes of secondary IgAN, supporting a mucosal source of nephritogenic IgA1. In the presence of microbial pathogens or food antigens, activated dendritic cells in the gut mucosa induce T-cell-dependent or T-cell-independent B-cell differentiation into IgA-secreting plasma cells. Herein we review the literature concerning mucosal immune function and how it is altered in this disease. We discuss recent evidence supporting a causal role of gut microbiota dysbiosis in IgAN pathogenesis.

Interactions of Nutrition and Infection: The Role of Micronutrient Deficiencies in the Immune Response to Pathogens and Implications for Child Health

Approximately five million children die each year from preventable causes, including respiratory infections, diarrhea, and malaria. Roughly half of those deaths are attributable to undernutrition, including micronutrient deficiencies (MNDs). The influence of infection on micronutrient status is well established: The inflammatory response to pathogens triggers anorexia, while pathogens and the immune response can both alter nutrient absorption and cause nutrient losses. We review the roles of vitamin A, vitamin D, iron, zinc, and selenium in the immune system, which act in the regulation of molecular- or cellular-level host defenses, directly affecting pathogens or protecting against oxidative stress or inflammation. We further summarize high-quality evidence regarding the synergistic or antagonistic interactions between MNDs, pathogens, and morbidity or mortality relevant to child health in low- and middle-income countries. We conclude with a discussion of gaps in the literature and future directions for multidisciplinary research on the interactions of MNDs, infection, and inflammation.

An overview of early genetic predictors of IgA deficiency

INTRODUCTION

Inborn errors of immunity (IEIs) refer to a heterogeneous category of diseases with defects in the number and/or function of components of the immune system. Immunoglobulin A (IgA) deficiency is the most prevalent IEI characterized by low serum level of IgA and normal serum levels of IgG and/or IgM. Most of the individuals with IgA deficiency are asymptomatic and are only identified through routine laboratory tests. Others may experience a wide range of clinical features including mucosal infections, allergies, and malignancies as the most important features. IgA deficiency is a multi-complex disease, and the exact pathogenesis of it is still unknown.

AREAS COVERED

This review compiles recent research on genetic and epigenetic factors that may contribute to the development of IgA deficiency. These factors include defects in B-cell development, IgA class switch recombination, synthesis, secretion, and the long-term survival of IgA switched memory B cells and plasma cells.

EXPERT OPINION

A better and more comprehensive understanding of the cellular pathways involved in IgA deficiency could lead to personalized surveillance and potentially curative strategies for affected patients, especially those with severe symptoms.

Crosstalk between gut microbiota and host immune system and its response to traumatic injury

Millions of microorganisms make up the complex microbial ecosystem found in the human gut. The immune system's interaction with the gut microbiota is essential for preventing inflammation and maintaining intestinal homeostasis. Numerous metabolic products that can cross-talk between immune cells and the gut epithelium are metabolized by the gut microbiota. Traumatic injury elicits a great and multifaceted immune response in the minutes after the initial offense, containing simultaneous pro- and anti-inflammatory responses. The development of innovative therapies that improve patient outcomes depends on the gut microbiota and immunological responses to trauma. The altered makeup of gut microbes, or gut dysbiosis, can also dysregulate immunological responses, resulting in inflammation. Major human diseases may become more common as a result of chronic dysbiosis and the translocation of bacteria and the products of their metabolism beyond the mucosal barrier. In this review, we briefly summarize the interactions between the gut microbiota and the immune system and human disease and their therapeutic probiotic formulations. We also discuss the immune response to traumatic injury.

Vitamin A-treated natural killer cells reduce interferon-gamma production and support regulatory T-cell differentiation

Natural killer (NK) cells are innate cytotoxic lymphocytes that contribute to immune responses against stressed, transformed, or infected cells. NK cell effector functions are regulated by microenvironmental factors, including cytokines, metabolites, and nutrients. Vitamin A is an essential micronutrient that plays an indispensable role in embryogenesis and development, but was also reported to regulate immune responses. However, the role of vitamin A in regulating NK cell functions remains poorly understood. Here, we show that the most prevalent vitamin A metabolite, all-trans retinoic acid (atRA), induces transcriptional and functional changes in NK cells leading to altered metabolism and reduced IFN-γ production in response to a wide range of stimuli. atRA-exposed NK cells display a reduced ability to support dendritic cell (DC) maturation and to eliminate immature DCs. Moreover, they support the polarization and proliferation of regulatory T cells. These results imply that in vitamin A-enriched environments, NK cells can acquire functions that might promote tolerogenic immunity and/or immunosuppression.

Simultaneous application of oral and intravaginal probiotics for Helicobacter pylori and its antibiotic-therapy-induced vaginal dysbacteriosis

Helicobacter pylori is a prevalent bacterial pathogen globally, implicated in various gastrointestinal disorders. Current recommended antibiotic therapies for H. pylori infection have been proven to be therapeutically insufficient, with low eradication rates and high recurrence rates. Emerging evidence suggests that antibiotic therapy for H. pylori can lead to gastrointestinal and subsequent vaginal dysbiosis, posing challenges for conventional antibiotic approaches. Thus, this article proposes a novel probiotic therapy involving simultaneous oral and intra-vaginal probiotic administration alongside antibiotics for H. pylori treatment, aiming to enhance eradication rates and mitigate dysbiosis. We begin by providing an overview of gastrointestinal and vaginal microbiota and their interconnectedness through the vagina-gut axis. We then review the efficacy of current antibiotic regimens for H. pylori and discuss how antibiotic treatment impacts the vaginal microenvironment. To explore the feasibility of this approach, we evaluate the effectiveness of oral and intra-vaginal probiotics in restoring normal microbiota in the gastrointestinal and vaginal tracts, respectively. Additionally, we analyze the direct mechanisms by which oral and intra-vaginal probiotics act on their respective tracts and discuss potential cross-tract mechanisms. Considering the potential synergistic therapeutic effects of probiotics in both the gastrointestinal and vaginal tracts, dual-channel probiotic therapy holds promise as a more effective approach for H. pylori eradication and dysbiosis mitigation, presenting a novel concept in the collaborative treatment of gastrointestinal and genital disorders.

Metabolic fitness of IgA+ plasma cells in the gut requires DOCK8

Dedicator of cytokinesis 8 (DOCK8) mutations lead to a primary immunodeficiency associated with recurrent gastrointestinal infections and poor antibody responses but, paradoxically, heightened IgE to food antigens, suggesting that DOCK8 is central to immune homeostasis in the gut. Using Dock8-deficient mice, we found that DOCK8 was necessary for mucosal IgA production to multiple T cell-dependent antigens, including peanut and cholera toxin. Yet DOCK8 was not necessary in T cells for this phenotype. Instead, B cell-intrinsic DOCK8 was required for maintenance of antigen-specific IgA-secreting plasma cells (PCs) in the gut lamina propria. Unexpectedly, DOCK8 was not required for early B cell activation, migration, or IgA class switching. An unbiased interactome screen revealed novel protein partners involved in metabolism and apoptosis. Dock8-deficient IgA+ B cells had impaired cellular respiration and failed to engage glycolysis appropriately. These results demonstrate that maintenance of the IgA+ PC compartment requires DOCK8 and suggest that gut IgA+ PCs have unique metabolic requirements for long-term survival in the lamina propria.

All-Trans-Retinoic Acid-Adjuvanted mRNA Vaccine Induces Mucosal Anti-Tumor Immune Responses for Treating Colorectal Cancer

Messenger RNA (mRNA) cancer vaccines are a new class of immunotherapies that can activate the immune system to recognize and destroy cancer cells. However, their effectiveness in treating colorectal cancer located on the mucosal surface of the gut is limited due to the insufficient activation of mucosal immune response and inadequate infiltration of cytotoxic T cells into tumors. To address this issue, a new mRNA cancer vaccine is developed that can stimulate mucosal immune responses in the gut by co-delivering all-trans-retinoic acid (ATRA) and mRNA using lipid nanoparticle (LNP). The incorporation of ATRA has not only improved the mRNA transfection efficiency of LNP but also induced high expression of gut-homing receptors on vaccine-activated T cells. Additionally, the use of LNP improves the aqueous solubility of ATRA, eliminating the need for toxic solvents to administer ATRA. Upon intramuscular injections, ATRA-adjuvanted mRNA-LNP significantly increase the infiltration of antigen-specific, cytotoxic T cells in the lamina propria of the intestine, mesenteric lymph nodes, and orthotopic colorectal tumors, resulting in significantly improved tumor inhibition and prolonged animal survival compared to conventional mRNA-LNP without ATRA. Overall, this study provides a promising approach for improving the therapeutic efficacy of mRNA cancer vaccines against colorectal cancer.

Maternal immunization and vitamin A sufficiency impact sow primary adaptive immunity and passive protection to nursing piglets against porcine epidemic diarrhea virus infection

Porcine epidemic diarrhea virus (PEDV) causes a highly contagious enteric disease with major economic losses to swine production worldwide. Due to the immaturity of the neonatal piglet immune system and given the high virulence of PEDV, improving passive lactogenic immunity is the best approach to protect suckling piglets against the lethal infection. We tested whether oral vitamin A (VA) supplementation and PEDV exposure of gestating and lactating VA-deficient (VAD) sows would enhance their primary immune responses and boost passive lactogenic protection against the PEDV challenge of their piglets. We demonstrated that PEDV inoculation of pregnant VAD sows in the third trimester provided higher levels of lactogenic protection of piglets as demonstrated by >87% survival rates of their litters compared with <10% in mock litters and that VA supplementation to VAD sows further improved the piglets' survival rates to >98%. We observed significantly elevated PEDV IgA and IgG antibody (Ab) titers and Ab-secreting cells (ASCs) in VA-sufficient (VAS)+PEDV and VAD+VA+PEDV sows, with the latter maintaining higher Ab titers in blood prior to parturition and in blood and milk throughout lactation. The litters of VAD+VA+PEDV sows also had the highest serum PEDV-neutralizing Ab titers at piglet post-challenge days (PCD) 0 and 7, coinciding with higher PEDV IgA ASCs and Ab titers in the blood and milk of their sows, suggesting an immunomodulatory role of VA in sows. Thus, sows that delivered sufficient lactogenic immunity to their piglets provided the highest passive protection against the PEDV challenge. Maternal immunization during pregnancy (± VA) and VA sufficiency enhanced the sow primary immune responses, expression of gut-mammary gland trafficking molecules, and passive protection of their offspring. Our findings are relevant to understanding the role of VA in the Ab responses to oral attenuated vaccines that are critical for successful maternal vaccination programs against enteric infections in infants and young animals.

Same yet different - how lymph node heterogeneity affects immune responses

Lymph nodes are secondary lymphoid organs in which immune responses of the adaptive immune system are initiated and regulated. Distributed throughout the body and embedded in the lymphatic system, local lymph nodes are continuously informed about the state of the organs owing to a constant drainage of lymph. The tissue-derived lymph carries products of cell metabolism, proteins, carbohydrates, lipids, pathogens and circulating immune cells. Notably, there is a growing body of evidence that individual lymph nodes differ from each other in their capacity to generate immune responses. Here, we review the structure and function of the lymphatic system and then focus on the factors that lead to functional heterogeneity among different lymph nodes. We will discuss how lymph node heterogeneity impacts on cellular and humoral immune responses and the implications for vaccination, tumour development and tumour control by immunotherapy.

Layer-by-layer nanoparticle encapsulating all-trans retinoic acid and CpG as a mucosal adjuvant targeting colorectal cancer

Colorectal cancer (CRC) ranks among the most prevalent cancers globally, demanding innovative therapeutic strategies. Immunotherapy, a promising avenue, employs cancer vaccines to activate the immune system against tumors. However, conventional approaches fall short of eliciting robust responses within the gastrointestinal (GI) tract, where CRC originates. Harnessing the potential of all-trans retinoic acid (ATRA) and cytosine-phosphorothioate-guanine (CpG), we developed layered nanoparticles using a layer-by-layer assembly method to co-deliver these agents. ATRA, crucial for gut immunity, was efficiently encapsulated alongside CpG within these nanoparticles. Administering these ATRA@CpG-NPs, combined with ovalbumin peptide (OVA), effectively inhibited orthotopic CRC growth in mice. Our approach leveraged the inherent benefits of ATRA and CpG, demonstrating superior efficacy in activating dendritic cells, imprinting T cells with gut-homing receptors, and inhibiting tumor growth. This mucosal adjuvant presents a promising strategy for CRC immunotherapy, showcasing the potential for targeting gut-associated immune responses in combating colorectal malignancies.

Immune cell trafficking: a novel perspective on the gut-skin axis

Immune cell trafficking, an essential mechanism for maintaining immunological homeostasis and mounting effective responses to infections, operates under a stringent regulatory framework. Recent advances have shed light on the perturbation of cell migration patterns, highlighting how such disturbances can propagate inflammatory diseases from their origin to distal organs. This review collates and discusses current evidence that demonstrates atypical communication between the gut and skin, which are conventionally viewed as distinct immunological spheres, in the milieu of inflammation. We focus on the aberrant, reciprocal translocation of immune cells along the gut-skin axis as a pivotal factor linking intestinal and dermatological inflammatory conditions. Recognizing that the translation of these findings into clinical practices is nascent, we suggest that therapeutic strategies aimed at modulating the axis may offer substantial benefits in mitigating the widespread impact of inflammatory diseases.

Gut-associated lymphoid tissue attrition associates with response to anti-α4β7 therapy in ulcerative colitis

Vedolizumab (VDZ) is a first-line treatment in ulcerative colitis (UC) that targets the α4β7- mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1) axis. To determine the mechanisms of action of VDZ, we examined five distinct cohorts of patients with UC. A decrease in naïve B and T cells in the intestines and gut-homing (β7+) plasmablasts in circulation of VDZ-treated patients suggested that VDZ targets gut-associated lymphoid tissue (GALT). Anti-α4β7 blockade in wild-type and photoconvertible (KikGR) mice confirmed a loss of GALT size and cellularity because of impaired cellular entry. In VDZ-treated patients with UC, treatment responders demonstrated reduced intestinal lymphoid aggregate size and follicle organization and a reduction of β7+IgG+ plasmablasts in circulation, as well as IgG+ plasma cells and FcγR-dependent signaling in the intestine. GALT targeting represents a previously unappreciated mechanism of action of α4β7-targeted therapies, with major implications for this therapeutic paradigm in UC.

Vitamin A deficiency impairs neutrophil-mediated control of Salmonella via SLC11A1 in mice

In sub-Saharan Africa, multidrug-resistant non-typhoidal Salmonella serovars are a common cause of fatal bloodstream infection. Malnutrition is a predisposing factor, but the underlying mechanisms are unknown. Here we show that vitamin A deficiency, one of the most prevalent micronutrient deficits afflicting African children, increases susceptibility to disseminated non-typhoidal Salmonella disease in mice and impairs terminal neutrophil maturation. Immature neutrophils had reduced expression of Slc11a1, a gene that encodes a metal ion transporter generally thought to restrict pathogen growth in macrophages. Adoptive transfer of SLC11A1-proficient neutrophils, but not SLC11A1-deficient neutrophils, reduced systemic Salmonella burden in Slc11a1-/- mice or mice with vitamin A deficiency. Loss of terminal granulopoiesis regulator CCAAT/enhancer-binding protein ϵ (C/EBPϵ) also decreased neutrophil-mediated control of Salmonella, but not that mediated by peritoneal macrophages. Susceptibility to infection increased in Cebpe-/- Slc11a1+/+ mice compared with wild-type controls, in an Slc11a1-expression-dependent manner. These data suggest that SLC11A1 deficiency impairs Salmonella control in part by blunting neutrophil-mediated defence.

Cellular and micro-environmental responses influencing the antitumor activity of all-trans retinoic acid in breast cancer

All-trans retinoic acid (ATRA) is the most relevant and functionally active metabolite of Vitamin-A. From a therapeutic standpoint, ATRA is the first example of pharmacological agent exerting its anti-tumor activity via a cell differentiating action. In the clinics, ATRA is used in the treatment of Acute Promyelocytic Leukemia, a rare form of myeloid leukemia with unprecedented therapeutic results. The extraordinary effectiveness of ATRA in the treatment of Acute Promyelocytic Leukemia patients has raised interest in evaluating the potential of this natural retinoid in the treatment of other types of neoplasias, with particular reference to solid tumors.The present article provides an overview of the available pre-clinical and clinical studies focussing on ATRA as a therapeutic agent in the context of breast cancer from a holistic point of view. In detail, we focus on the direct effects of ATRA in breast cancer cells as well as the underlying molecular mechanisms of action. In addition, we summarize the available information on the action exerted by ATRA on the breast cancer micro-environment, an emerging determinant of the progression and invasive behaviour of solid tumors. In particular we discuss the recent evidences of ATRA activity on the immune system. Finally, we analyse and discuss the results obtained with the few ATRA-based clinical trials conducted in the context of breast cancer.

Polysaccharide from Atractylodes macrocephala Koidz Binding with Zinc Oxide Nanoparticles as a Novel Mucosal Immune Adjuvant for H9N2 Inactivated Vaccine

H9N2 avian influenza poses a significant public health risk, necessitating effective vaccines for mass immunization. Oral inactivated vaccines offer advantages like the ease of administration, but their efficacy often requires enhancement through mucosal adjuvants. In a previous study, we established a novel complex of polysaccharide from Atractylodes macrocephala Koidz binding with zinc oxide nanoparticles (AMP-ZnONPs) and preliminarily demonstrated its immune-enhancing function. This work aimed to evaluate the efficacy of AMP-ZnONPs as adjuvants in an oral H9N2-inactivated vaccine and the vaccine's impact on intestinal mucosal immunity. In this study, mice were orally vaccinated on days 0 and 14 after adapting to the environment. AMP-ZnONPs significantly improved HI titers, the levels of specific IgG, IgG1 and IgG2a in serum and sIgA in intestinal lavage fluid; increased the number of B-1 and B-2 cells and dendritic cell populations; and enhanced the mRNA expression of intestinal homing factors and immune-related cytokines. Interestingly, AMP-ZnONPs were more likely to affect B-1 cells than B-2 cells. AMP-ZnONPs showed mucosal immune enhancement that was comparable to positive control (cholera toxin, CT), but not to the side effect of weight loss caused by CT. Compared to the whole-inactivated H9N2 virus (WIV) group, the WIV + AMP-ZnONP and WIV + CT groups exhibited opposite shifts in gut microbial abundance. AMP-ZnONPs serve as an effective and safe mucosal adjuvant for oral WIV, improving cellular, humoral and mucosal immunity and microbiota in the gastrointestinal tract, avoiding the related undesired effects of CT.

Follicular Helper T Cells in Peyer's Patches and Galactose- Deficient Iga1 Contribute to Iga Nephropathy

BACKGROUND

Common primary glomerulonephritis with aberrant mucosal immunity is IgA nephropathy (IgAN). T follicular helper (TFH) cells are essential in regulating B cell differentiation. Peyer's patches (PPs) are the main site where IgA+ plasmablasts differentiate.

OBJECTIVE

Our study aimed to investigate the TFH cell's potential contribution to the etiology of IgA nephropathy.

METHODS

In PPs from IgAN mouse models, the ratio of the TFH cell, B220+IgA+, B220+IgM+, and B220-IgA+ lymphocytes were assessed. Then, we used Western blot to assess the expression of Bcl-6, Blimp- 1, and IL-21 proteins in PPs and used RTPCR to assess the expression of IL-21 and TGF-β1 mRNA. TFH cells coculture with spleen cells to measure the degree of IL-21 and the ratio of activation marker CD69 on the TFH cells. Naive B cells (CD27-IgD+) from children suffering from IgAN were cultured with TFH cell-related cytokines. The supernatant was detected to assess the excretion of galactose-deficient IgA1 (Gd-IgA1).

RESULTS

IgAN mice developed noticeably increased degrees of IL-21 and CD69 on TFH cells than controls did, as well as higher percentages of B220+IgA+, B220+IgM+, B220+IgA+, TGF- β1, and IL-21 mRNA and Bcl-6, IL-21 proteins in PPs. The Gd-IgA1 level in the supernatant and IgAN- positive children's serum were noticeably higher than those of the healthy controls (P < 0.05). PPs provide the microenvironment to induce the production of IgA-secreting plasmablasts.

CONCLUSION

TFH cells may be a key moderator to induce B cell differentiation into IgAsecreting plasmablasts and produce Gd-IgA1, which plays a significant part in IgAN's pathogenesis. It could be a new therapeutic target in the future.

Oral Administration of Cancer Vaccines: Challenges and Future Perspectives

Cancer vaccines, a burgeoning strategy in cancer treatment, are exploring innovative administration routes to enhance patient and medical staff experiences, as well as immunological outcomes. Among these, oral administration has surfaced as a particularly noteworthy approach, which is attributed to its capacity to ignite both humoral and cellular immune responses at systemic and mucosal tiers, thereby potentially bolstering vaccine efficacy comprehensively and durably. Notwithstanding this, the deployment of vaccines through the oral route in a clinical context is impeded by multifaceted challenges, predominantly stemming from the intricacy of orchestrating effective oral immunogenicity and necessitating strategic navigation through gastrointestinal barriers. Based on the immunogenicity of the gastrointestinal tract, this review critically analyses the challenges and recent advances and provides insights into the future development of oral cancer vaccines.

Vitamin A and vitamin D induced nuclear hormone receptor activation and its impact on B cell differentiation and immunoglobulin production

Vitamin A and vitamin D metabolites are ligands to nuclear receptors - namely RAR, RXR and VDR. The activation of these receptors in human B cells impacts B cell maturation and function. In this review, we discuss how 9-cis retinoic acid (9cRA) and 1,25-dihydroxyvitamin D3 (calcitriol) individually or in conjunction, signal through their nuclear receptors and thereby impact B cell differentiation, immunoglobulin class switching to IgA at the expense of IgE, and also B cell migration and homing. Impact of the vitamin metabolites individually on B cell survival factors are well elucidated, be it the regulation of BAFF and APRIL, the induction of TGF-β or suppression of NF-κB. Very little is known about the impact of 9cRA and calcitriol together on B cells. Recently our group revealed that 9cRA and calcitriol together in the context of the B cell differentiation, induces naïve B cell differentiation into IgA+ plasmablasts, the functional and underlying molecular regulations however require further investigation. In conclusion, the conjunctional impact of these nuclear receptor ligands on B cell functionality is important to better understand B cell dependent clinical outcomes in allergy and autoimmunity. Within this review, we hypothesize that a balance between both vitamins is of utmost importance to provide a robust humoral immune response and a better treatment of disorders characterised by dysregulated immune responses such as IgE-dependent allergy or autoimmunity such as lupus erythematosus.

Autoreactive B cells in rheumatoid arthritis include mainly activated CXCR3+ memory B cells and plasmablasts

Many autoimmune diseases (AIDs) are characterized by the persistence of autoreactive B cell responses, which have been directly implicated in disease pathogenesis. How and why these cells are generated or how they are maintained for years is largely unknown. Rheumatoid arthritis (RA) is among the most common AIDs and is characterized by autoantibodies recognizing proteins with posttranslational modifications (PTMs). This PTM-directed autoreactive B cell compartment is ill defined. Here, we visualized the B cell response against the three main types of PTM antigens implicated in RA by spectral flow cytometry. Our results showed extensive cross-reactivity of PTM-directed B cells against all three PTM antigens (citrulline, homocitrulline, and acetyllysine). Unsupervised clustering revealed several distinct memory B cell (mBC) populations. PTM-directed cells clustered with the most recently activated class-switched mBC phenotype, with high CD80, low CD24, and low CD21 expression. Notably, patients also harbored large fractions of PTM-directed plasmablasts (PBs). Both PTM-directed mBCs and PBs showed high expression of CXCR3, a receptor for chemokines present in abundance in arthritic joints. Together, our data provide detailed insight into the biology of B cell autoreactivity and its remarkable, seemingly exhaustless persistence in a prominent human AID.

HIV-1 treatment timing shapes the human intestinal memory B-cell repertoire to commensal bacteria

HIV-1 infection causes severe alterations of gut mucosa, microbiota and immune system, which can be curbed by early antiretroviral therapy. Here, we investigate how treatment timing affects intestinal memory B-cell and plasmablast repertoires of HIV-1-infected humans. We show that only class-switched memory B cells markedly differ between subjects treated during the acute and chronic phases of infection. Intestinal memory B-cell monoclonal antibodies show more prevalent polyreactive and commensal bacteria-reactive clones in late- compared to early-treated individuals. Mirroring this, serum IgA polyreactivity and commensal-reactivity are strongly increased in late-treated individuals and correlate with intestinal permeability and systemic inflammatory markers. Polyreactive blood IgA memory B cells, many of which egressed from the gut, are also substantially enriched in late-treated individuals. Our data establish gut and systemic B-cell polyreactivity to commensal bacteria as hallmarks of chronic HIV-1 infection and suggest that initiating treatment early may limit intestinal B-cell abnormalities compromising HIV-1 humoral response.

The Role of IgA in the Manifestation and Prevention of Allergic Immune Responses

PURPOSE OF REVIEW

Immunoglobulin A (IgA) mediates immune exclusion of antigens in the gut. Notably, IgA plays also a role in the prevention of IgE-mediated allergies and induction of immune tolerance. The present review addresses the role of IgA in the manifestation of IgE-mediated allergies, including allergen-specific immunotherapy (AIT), the regulation of IgA production, and the mechanism of IgA in immune cell activation.

RECENT FINDINGS

The majority of studies report an association of IgA with the induction of immune tolerance in IgE-mediated allergies. However, reports on the involvement of humoral and mucosal IgA, IgA subtypes, monomeric and polymeric IgA, and the mechanism of IgA-mediated immune cell activation are confounding. Effects by IgA are likely mediated by alteration of microbiota, IgE-blocking capacity, or activation of inhibitory signaling pathways. However, the precise mechanism of IgA-regulation, the contribution of serum and/or mucosal IgA, and IgA1/2 subtypes, on the manifestation of IgE-mediated allergies, and the underlying immune modulatory mechanism are still elusive.

Impact of intestinal microenvironments in obesity and bariatric surgery on shaping macrophages

Obesity is associated with alterations in tissue composition, systemic cellular metabolism, and low-grade chronic inflammation. Macrophages are heterogenous innate immune cells ubiquitously localized throughout the body and are key components of tissue homeostasis, inflammation, wound healing, and various disease states. Macrophages are highly plastic and can switch their phenotypic polarization and change function in response to their local environments. Here, we discuss how obesity alters the intestinal microenvironment and potential key factors that can influence intestinal macrophages as well as macrophages in other organs, including adipose tissue and hematopoietic organs. As bariatric surgery can induce metabolic adaptation systemically, we discuss the potential mechanisms through which bariatric surgery reshapes macrophages in obesity.

Recruitment and Residence of Intestinal T Cells - Lessons for Therapy in Inflammatory Bowel Disease

Targeting leukocyte trafficking in the management of inflammatory bowel disease [IBD] has been a significant therapeutic advance over the past 15 years. However, as with other advanced therapies, phase III clinical trials report response to trafficking inhibitors in only a proportion of patients, with fewer achieving clinical remission or mucosal healing. Additionally, there have been significant side effects, most notably progressive multifocal leukoencephalopathy in association with the α4 inhibitor natalizumab. This article reviews the mechanisms underpinning T cell recruitment and residence, to provide a background from which the strength and limitations of agents that disrupt leukocyte trafficking can be further explored. The therapeutic impact of trafficking inhibitors is underpinned by the complexity and plasticity of the intestinal immune response. Pathways essential for gut homing in health may be bypassed in the inflamed gut, thus providing alternative routes of entry when conventional homing molecules are targeted. Furthermore, there is conservation of trafficking architecture between proinflammatory and regulatory T cells. The persistence of resident memory cells within the gut gives rise to local established pro-inflammatory populations, uninfluenced by inhibition of trafficking. Finally, trafficking inhibitors may give rise to effects beyond the intended response, such as the impact of vedolizumab on innate immunity, as well as on target side effects. With significant research efforts into predictive biomarkers already underway, it is ultimately hoped that a better understanding of trafficking and residence will help us predict which patients are most likely to respond to inhibition of leukocyte trafficking, and how best to combine therapies.

Nanoparticle oral absorption and its clinical translational potential

Oral administration of pharmaceuticals is the most preferred route of administration for patients, but it is challenging to effectively deliver active ingredients (APIs) that i) have extremely high or low solubility in intestinal fluids, ii) are large in size, iii) are subject to digestive and/or metabolic enzymes present in the gastrointestinal tract (GIT), brush border, and liver, and iv) are P-glycoprotein substrates. Over the past decades, efforts to increase the oral bioavailability of APIs have led to the development of nanoparticles (NPs) with non-specific uptake pathways (M cells, mucosal, and tight junctions) and target-specific uptake pathways (FcRn, vitamin B12, and bile acids). However, voluminous findings from preclinical models of different species rarely meet practical standards when translated to humans, and API concentrations in NPs are not within the adequate therapeutic window. Various NP oral delivery approaches studied so far show varying bioavailability impacted by a range of factors, such as species, GIT physiology, age, and disease state. This may cause difficulty in obtaining similar oral delivery efficacy when research results in animal models are translated into humans. This review describes the selection of parameters to be considered for translational potential when designing and developing oral NPs.

Peyer's patch phagocytes acquire specific transcriptional programs that influence their maturation and activation profiles

Peyer's patches (PPs) are secondary lymphoid organs in contact with the external environment via the intestinal lumen, thus combining antigen sampling and immune response initiation sites. Therefore, they provide a unique opportunity to study the entire process of phagocyte differentiation and activation in vivo. Here, we deciphered the transcriptional and spatial landscape of PP phagocyte populations from their emergence in the tissue to their final maturation state at homeostasis and under stimulation. Activation of monocyte-derived Lysozyme-expressing dendritic cells (LysoDCs) differs from that of macrophages by their upregulation of conventional DC (cDC) signature genes such as Ccr7 and downregulation of typical monocyte-derived cell genes such as Cx3cr1. We identified gene sets that distinguish PP cDCs from the villus ones and from LysoDCs. We also identified key immature, early, intermediate, and late maturation markers of PP phagocytes. Finally, exploiting the ability of the PP interfollicular region to host both villous and subepithelial dome emigrated cDCs, we showed that the type of stimulus, the subset, but also the initial location of cDCs shape their activation profile and thus direct the immune response. Our study highlights the importance of targeting the right phagocyte subset at the right place and time to manipulate the immune response.

The Underappreciated Role of Secretory IgA in IBD

Eighty percent of antibody secreting cells (ASCs) are found in the intestine, where they produce grams of immunoglobulin (Ig) A daily. immunoglobulin A is actively transcytosed into the lumen, where it plays a critical role in modulating the gut microbiota. Although loss of immune tolerance to bacterial antigens is the likely trigger of the dysregulated immune response that characterizes inflammatory bowel disease (IBD), little effort has been placed on understanding the interface between B cells, IgA, and the microbiota during initiation or progression of disease. This may be in part due to the misleading fact that IgA-deficient humans are mostly asymptomatic, likely due to redundant role of secretory (S) IgM. Intestinal B cell recruitment is critically dependent on integrin α4β7-MAdCAM-1 interactions, yet antibodies that target α4β7 (ie, vedolizumab), MAdCAM-1 (ie, ontamalimab), or both β7 integrins (α4β7 and αE [CD103] β7; etrolizumab) are in clinical use or development as IBD therapeutics. The effect of such interventions on the biology of IgA is largely unknown, yet a single dose of vedolizumab lowers SIgA levels in stool and weakens the oral immunization response to cholera vaccine in healthy volunteers. Thus, it is critical to further understand the role of these integrins for the migration of ASC and other cellular subsets during homeostasis and IBD-associated inflammation and the mode of action of drugs that interfere with this traffic. We have recently identified a subset of mature ASC that employs integrin αEβ7 to dock with intestinal epithelial cells, predominantly in the pericryptal region of the terminal ileum. This role for the integrin had not been appreciated previously, nor the αEβ7-dependent mechanism of IgA transcytosis that it supports. Furthermore, we find that B cells more than T cells are critically dependent on α4β7-MAdCAM-1 interactions; thus MAdCAM-1 blockade and integrin-β7 deficiency counterintuitively hasten colitis in interleukin-10-deficient mice. In both cases, de novo recruitment of IgA ASC to the intestinal lamina propria is compromised, leading to bacterial overgrowth, dysbiosis, and lethal colitis. Thus, despite the safe and effective use of anti-integrin antibodies in patients with IBD, much remains to be learned about their various cell targets.

Microbial Reprogramming in Obsessive-Compulsive Disorders: A Review of Gut-Brain Communication and Emerging Evidence

Obsessive-compulsive disorder (OCD) is a debilitating mental health disorder characterized by intrusive thoughts (obsessions) and repetitive behaviors (compulsions). Dysbiosis, an imbalance in the gut microbial composition, has been associated with various health conditions, including mental health disorders, autism, and inflammatory diseases. While the exact mechanisms underlying OCD remain unclear, this review presents a growing body of evidence suggesting a potential link between dysbiosis and the multifaceted etiology of OCD, interacting with genetic, neurobiological, immunological, and environmental factors. This review highlights the emerging evidence implicating the gut microbiota in the pathophysiology of OCD and its potential as a target for novel therapeutic approaches. We propose a model that positions dysbiosis as the central unifying element in the neurochemical, immunological, genetic, and environmental factors leading to OCD. The potential and challenges of microbial reprogramming strategies, such as probiotics and fecal transplants in OCD therapeutics, are discussed. This review raises awareness of the importance of adopting a holistic approach that considers the interplay between the gut and the brain to develop interventions that account for the multifaceted nature of OCD and contribute to the advancement of more personalized approaches.

Retinoic Acid Signaling Is Required for Dendritic Cell Maturation and the Induction of T Cell Immunity

Vitamin A and its biologically active metabolites, all-trans and 9-cis retinoic acid (RA), are thought to be important in generating and modulating immune function. However, RA modulates the function of many types of immune cells, and its specific role in dendritic cell (DC) activation, Ag presentation, and T cell effector function has not been fully characterized. Because RA works primarily through RA receptor (RAR)α, we examined mice with a myeloid cell-specific defect in RA signaling. These transgenic mice have a CD11c-cre-driven expression of a truncated form of RARα that specifically blocks the signaling of all forms of RARs in myeloid cells. This defect results in abnormal DC function, with impaired DC maturation and activation, and reduced Ag uptake and processing. These DC abnormalities were associated with a reduced ability to mount Ag-specific T cell responses to immunization despite having normally functioning T cells. In contrast, the loss of DC-specific RA signaling did not significantly alter levels of Ag-specific Abs postimmunization and resulted in an increase in bronchial IgA. Our findings indicate that RA signaling in DCs is crucial for immune activation, and its absence impairs the development of Ag-specific effector functions of T cell immunity.

Vitamin A deficiency and vitamin A supplementation affect innate and T cell immune responses to rotavirus A infection in a conventional sow model

Rotavirus A (RVA) causes ~200,000 diarrheal deaths annually in children <5yrs, mostly in low- and middle-income countries. Risk factors include nutritional status, social factors, breastfeeding status, and immunodeficiency. We evaluated the effects of vitamin A (VA) deficiency/VA supplementation and RVA exposure (anamnestic) on innate and T cell immune responses in RVA seropositive pregnant and lactating sows and passive protection of their piglets post-RVA challenge. Sows were fed VA deficient (VAD) or sufficient (VAS) diets starting at gestation day (GD)30. A subset of VAD sows received VA supplementation from GD|76 (30,000IU/day, VAD+VA). Sows (6 groups) were inoculated with porcine RVA G5P[7] (OSU strain) or Minimal Essential Medium (mock) at GD~90: VAD+RVA; VAS+RVA; VAD+VA+RVA; VAD-mock; VAS-mock; and VAD+VA-mock. Blood, milk, and gut-associated tissues were collected from sows at several time points to examine innate [natural killer (NK), dendritic (DC) cells], T cell responses and changes in genes involved in the gut-mammary gland (MG)-immunological axis trafficking. Clinical signs of RVA were evaluated post inoculation of sows and post-challenge of piglets. We observed decreased frequencies of NK cells, total and MHCII+ plasmacytoid DCs, conventional DCs, CD103+ DCs and CD4+/CD8+ and T regulatory cells (Tregs) and NK cell activity in VAD+RVA sows. Polymeric Ig receptor and retinoic acid receptor alpha (RARα) genes were downregulated in mesenteric lymph nodes and ileum of VAD+RVA sows. Interestingly, RVA-specific IFN-γ producing CD4+/CD8+ T cells were increased in VAD-Mock sows, coinciding with increased IL-22 suggesting inflammation in these sows. VA supplementation to VAD+RVA sows restored frequencies of NK cells and pDCs, and NK activity, but not tissue cDCs and blood Tregs. In conclusion, similar to our recent observations of decreased B cell responses in VAD sows that led to decreased passive immune protection of their piglets, VAD impaired innate and T cell responses in sows, while VA supplementation to VAD sows restored some, but not all responses. Our data reiterate the importance of maintaining adequate VA levels and RVA immunization in pregnant and lactating mothers to achieve optimal immune responses, efficient function of the gut-MG-immune cell-axis and to improve passive protection of their piglets.

Intestinal Peyer's Patches: Structure, Function, and In Vitro Modeling

BACKGOUND

Considering the important role of the Peyer's patches (PPs) in gut immune balance, understanding of the detailed mechanisms that control and regulate the antigens in PPs can facilitate the development of immune therapeutic strategies against the gut inflammatory diseases.

METHODS

In this review, we summarize the unique structure and function of intestinal PPs and current technologies to establish in vitro intestinal PP system focusing on M cell within the follicle-associated epithelium and IgA⁺ B cell models for studying mucosal immune networks. Furthermore, multidisciplinary approaches to establish more physiologically relevant PP model were proposed.

RESULTS

PPs are surrounded by follicle-associated epithelium containing microfold (M) cells, which serve as special gateways for luminal antigen transport across the gut epithelium. The transported antigens are processed by immune cells within PPs and then, antigen-specific mucosal immune response or mucosal tolerance is initiated, depending on the response of underlying mucosal immune cells. So far, there is no high fidelity (patho)physiological model of PPs; however, there have been several efforts to recapitulate the key steps of mucosal immunity in PPs such as antigen transport through M cells and mucosal IgA responses.

CONCLUSION

Current in vitro PP models are not sufficient to recapitulate how mucosal immune system works in PPs. Advanced three-dimensional cell culture technologies would enable to recapitulate the function of PPs, and bridge the gap between animal models and human.