Secretory IgA: arresting microbial pathogens at epithelial borders

Requirement of a Wnt5A-microbiota axis in the maintenance of gut B-cell repertoire and protection from infection

We investigated the influence of a Wnt5A-gut microbiota axis on gut B-cell repertoire and protection from infection, having previously demonstrated that Wnt5A in association with gut commensals helps shape gut T-cell repertoire. Accordingly, Wnt5A heterozygous mice, which express less than wild-type level of Wnt5A, and their isolated Peyer's patches (PPs) were studied in comparison with the wild-type counterparts. The percentages of IgM- and IgA-expressing B cells were quite similar in the PP of both sets of mice. However, the PP of the Wnt5A heterozygous mice harbored significantly higher than wild-type levels of microbiota-bound B cell-secreted IgA, indicating the prevalence of a microbial population therein, which is significantly altered from that of wild-type. Additionally, the percentage of PP IgG1-expressing B cells was appreciably depressed in the Wnt5A heterozygous mice in comparison to wild-type. Wnt5A heterozygous mice, furthermore, exhibited notably higher than the wild-type levels of morbidity and mortality following infection with Salmonella typhimurium, a common gut pathogen. Differences in morbidity/mortality correlated with considerable disparity between the PP-B-cell repertoires of the Salmonella-infected Wnt5A heterozygous and wild-type mice, in which the percentage of IgG1-expressing B1b cells in the PP of heterozygous mice remains significantly low as compared to wild-type. Overall, these results suggest that a gut Wnt5A-microbiota axis is intrinsically associated with the maintenance of gut B-cell repertoire and protection from infection.IMPORTANCEAlthough it is well accepted that B cells and microbiota are required for protection from infection and preservation of gut health, a lot remains unknown about how the optimum B-cell repertoire and microbiota are maintained in the gut. The importance of this study lies in the fact that it unveils a potential role of a growth factor termed Wnt5A in the safeguarding of the gut B-cell population and microbiota, thereby protecting the gut from the deleterious effect of infections by common pathogens. Documentation of the involvement of a Wnt5A-microbiota axis in the shaping of a protective gut B-cell repertoire, furthermore, opens up new avenues of investigations for understanding gut disorders related to microbial dysbiosis and B-cell homeostasis that, till date, are considered incurable.

Purification of secretory IgA monoclonal antibodies enriched fraction directly from cell culture medium using aqueous two-phase systems

Secretory immunoglobulin A [sIgA] is a promising candidate for enteric therapeutics applications, and several sIgA-based constructs are currently being developed by groups utilizing clarified Chinese hamster ovary [CHO] cell culture supernatants. To the monoclonal antibody downstream processing typically entails chromatography-based purification processes beginning with Protein A chromatography. In this paper, aqueous two-phase systems [ATPS] were employed for the preliminary purification of secretory immunoglobulin A [sIgA] monoclonal antibody [mAb] from clarified CHO-cell culture supernatants. A 24 full factorial design was utilized. The influence of various process parameters such as pH, PEG molecular weight [MPEG], PEG concentration [CPEG], and phosphate salt concentration [CPHO], on the sIgA partition coefficient [K sIgA] and the recovery index [Y] in the PEG phase were evaluated. The Elisa assay revealed that, in the ATPS conditions tested, sIgA mAb was mostly detected in PEG upper phase. Run 14 with the highest sIgA activity exhibited the following conditions: MPEG 8.000 g/mol, CPEG 12,5 %, pH 7,0 and CPHO 10 %, and a sIgA K of 94.50 and a recovery index [Y] of 33.52 %. The proposed platform provides straightforward implementation, yields comparable results, and offers significantly improved economics for manufacturing sIgA mAb biotherapeutics.

Mucoadhesive film for oral delivery of vaccines for protection of the respiratory tract

The delivery of vaccines plays a pivotal role in influencing the strength and longevity of the immune response and controlling reactogenicity. Mucosal immunization, as compared to parenteral vaccination, could offer greater protection against respiratory infections while being less invasive. While oral vaccination has been presumed less effective and believed to target mainly the gastrointestinal tract, trans-buccal delivery using mucoadhesive films (MAF) may allow targeted delivery to the mucosa. Here we present an effective strategy for mucosal delivery of several vaccine platforms incorporated in MAF, including DNA plasmids, viral vectors, and lipid nanoparticles incorporating mRNA (mRNA/LNP). The mRNA/LNP vaccine formulation targeting SARS-CoV-2 as a proof of concept remained stable within MAF consisting of slowly releasing water-soluble polymers and an impermeable backing layer, facilitating enhanced penetration into the oral mucosa. This formulation elicited antibody and cellular responses comparable to the intramuscular injection, but also induced the production of mucosal IgAs, highlighting its efficacy, particularly for use as a booster vaccine and the potential advantage for protection against respiratory infections. The MAF vaccine preparation demonstrates significant advantages, such as efficient delivery, stability, and simple noninvasive administration with the potential to alleviate vaccine hesitancy.

Effect of hospitalization on equine local intestinal immunoglobulin A (IgA) concentration measured in feces

During hospitalization horses may develop gastrointestinal conditions triggered by a stress-associated weak local immune system. The prospective, clinical trial was conducted to find out whether fecal immunoglobulin A (IgA) concentrations could be determined in hospitalized horses and how they changed during hospitalization and in response to various stressors. Samples were obtained from 110 horses and a control group (n = 14). At arrival in the hospital, horses were categorized into pain grades (1-5), and elective versus strenuous surgery (> 2 hours, traumatic and emergency procedures). Feces were collected on day 1, day 2, day 3, and day 7 in all horses. Blood samples were obtained at the same intervals, but additionally after general anaesthesia in horses undergoing surgery (day 2). IgA concentration in feces was determined by ELISA and measured in optical density at 450nm. The control group showed constant IgA concentrations on all days (mean value 0.30 OD450 ±SD 0.11, 1.26 mg/g; n = 11). After general anaesthesia fecal IgA concentrations decreased considerably independent of duration and type of surgery (P < 0.001 for elective and P = 0.043 for traumatic surgeries). High plasma cortisol concentrations were weakly correlated with low fecal IgA on the day after surgery (P = 0.012, day 3, correlation coefficient r = 0.113). Equine fecal IgA concentrations showed a decline associated with transport, surgery, and hospitalization in general, indicating that stress has an impact on the local intestinal immune function and may predispose horses for developing gastrointestinal diseases such as enterocolitis.

Recombinant neutralizing secretory IgA antibodies for preventing mucosal acquisition and transmission of SARS-CoV-2

Passive delivery of antibodies to mucosal sites may be a valuable adjunct to COVID-19 vaccination to prevent infection, treat viral carriage, or block transmission. Neutralizing monoclonal IgG antibodies are already approved for systemic delivery, and several clinical trials have been reported for delivery to mucosal sites where SARS-CoV-2 resides and replicates in early infection. However, secretory IgA may be preferred because the polymeric complex is adapted for the harsh, unstable external mucosal environment. Here, we investigated the feasibility of producing neutralizing monoclonal IgA antibodies against SARS-CoV-2. We engineered two class-switched mAbs that express well as monomeric and secretory IgA (SIgA) variants with high antigen-binding affinities and increased stability in mucosal secretions compared to their IgG counterparts. SIgAs had stronger virus neutralization activities than IgG mAbs and were protective against SARS-CoV-2 infection in an in vivo murine model. Furthermore, SIgA1 can be aerosolized for topical delivery using a mesh nebulizer. Our findings provide a persuasive case for developing recombinant SIgAs for mucosal application as a new tool in the fight against COVID-19.

Immunoglobulin A response to SARS-CoV-2 infection and immunity

The novel coronavirus disease (COVID-19) and its infamous "Variants" of the etiological agent termed Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) has proven to be a global health concern. The three antibodies, IgA, IgM, and IgG, perform their dedicated role as main workhorses of the host adaptive immune system in virus neutralization. Immunoglobulin-A (IgA), also known as "Mucosal Immunoglobulin", has been under keen interest throughout the viral infection cycle. Its importance lies because IgA is predominant mucosal antibody and SARS family viruses primarily infect the mucosal surfaces of human respiratory tract. Therefore, IgA can be considered a diagnostic and prognostic marker and an active infection biomarker for SARS CoV-2 infection. Along with molecular analyses, serological tests, including IgA detection tests, are gaining ground in application as an early detectable marker and as a minimally invasive detection strategy. In the current review, it was emphasized the role of IgA response in diagnosis, host defense strategies, treatment, and prevention of SARS-CoV-2 infection. The data analysis was performed through almost 100 published peer-reviewed research reports and comprehended the importance of IgA in antiviral immunity against SARS-CoV-2 and other related respiratory viruses. Taken together, it is concluded that secretory IgA- Abs can serve as a promising detection tool for respiratory viral diagnosis and treatment parallel to IgG-based therapeutics and diagnostics. Vaccine candidates that target and trigger mucosal immune response may also be employed in future dimensions of research against other respiratory viruses.

Dietary fiber pectin: challenges and potential anti-inflammatory benefits for preterms and newborns

Pectins, a class of dietary fibers abundant in vegetables and fruits, have drawn considerable interest due to their potential anti-inflammatory properties. Numerous studies have indicated that incorporating pectins into infant formula could be a safe strategy for alleviating infant regurgitation and diarrhea. Moreover, pectins have been shown to modulate cytokine production, macrophage activity, and NF-kB expression, all contributing to their anti-inflammatory effects. Despite this promising evidence, the exact mechanisms through which pectins exert these functions and how their structural characteristics influence these processes remain largely unexplored. This knowledge is particularly significant in the context of gut inflammation in developing preterm babies, a critical aspect of necrotizing enterocolitis (NEC), and in children and adults dealing with inflammatory bowel disease (IBD). Our mini review aims to provide an up-to-date compilation of relevant research on the effects of pectin on gut immune responses, specifically focusing on preterms and newborns. By shedding light on the underlying mechanisms and implications of pectin-mediated anti-inflammatory properties, this review seeks to advance our knowledge in this area and pave the way for future research and potential therapeutic interventions.

Role of Gut Microbiota, Immune Imbalance, and Allostatic Load in the Occurrence and Development of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a prevailing complication arising from diabetes mellitus. Unfortunately, there are no trustworthy and efficacious treatment modalities currently available. In recent times, compelling evidence has emerged regarding the intricate correlation between the kidney and the gut microbiota, which is considered the largest immune organ within the human physique. Various investigations have demonstrated that the perturbation of the gut microbiota and its associated metabolites potentially underlie the etiology and progression of DKD. This phenomenon may transpire through perturbation of both the innate and the adaptive immunity, leading to a burdensome allostatic load on the body and ultimately culminating in the development of DKD. Within this literature review, we aim to delve into the intricate interplay between the gut microbiota, its metabolites, and the immune system in the context of DKD. Furthermore, we strive to explore and elucidate potential chemical interventions that could hold promise for the treatment of DKD, thereby offering invaluable insights and directions for future research endeavors.

Gut commensals and their metabolites in health and disease

Purpose of review

This review comprehensively discusses the role of the gut microbiome and its metabolites in health and disease and sheds light on the importance of a holistic approach in assessing the gut.

Recent findings

The gut microbiome consisting of the bacteriome, mycobiome, archaeome, and virome has a profound effect on human health. Gut dysbiosis which is characterized by perturbations in the microbial population not only results in gastrointestinal (GI) symptoms or conditions but can also give rise to extra-GI manifestations. Gut microorganisms also produce metabolites (short-chain fatty acids, trimethylamine, hydrogen sulfide, methane, and so on) that are important for several interkingdom microbial interactions and functions. They also participate in various host metabolic processes. An alteration in the microbial species can affect their respective metabolite concentrations which can have serious health implications. Effective assessment of the gut microbiome and its metabolites is crucial as it can provide insights into one's overall health.

Summary

Emerging evidence highlights the role of the gut microbiome and its metabolites in health and disease. As it is implicated in GI as well as extra-GI symptoms, the gut microbiome plays a crucial role in the overall well-being of the host. Effective assessment of the gut microbiome may provide insights into one's health status leading to more holistic care.

Small intestinal bacterial overgrowth: current update

PURPOSE OF REVIEW

This article aims to provide an up-to-date review of small intestinal bacterial overgrowth (SIBO), including etiology and risk factors, clinical manifestations, diagnostic evaluation for suspected SIBO, and therapeutic options.

RECENT FINDINGS

Recent advances in breath testing, capsule and urine-based testing have opened new avenues and improved diagnostic yield of SIBO. Nonantibiotic-based treatment strategies have shown promising results in initial trials.

SUMMARY

Small intestinal bacterial overgrowth (SIBO) is a condition defined by the excess bacteria or changes in bacterial composition of the small intestine. These are associated with various gastrointestinal (GI) symptoms such as bloating, abdominal distension, diarrhea, nutrient deficiencies, and even frank weight loss. Small bowel jejunal aspirate of >10 5 CFU/ml has traditionally been considered the gold standard for diagnosis. Glucose and lactulose breath testing have become more common in clinical practice as they are noninvasive, easily accessible, and have lower cost. Treatment focuses on the eradication of excess bacteria in the small bowel and is traditionally done with the use of oral antibiotics. Other emerging therapies may include probiotics, diet manipulation, and prokinetic agents.

Fetal Secretory IgA Delivery via Transamniotic Fetal Immunotherapy (TRAFIT) in a Rodent Model

PURPOSE

We sought to determine the feasibility and routing kinetics of transamniotic fetal delivery of secretory immunoglobulin-A (SIgA), in a rodent model.

METHODS

Fetuses (n = 94) from seven time-dated pregnant dams received intra-amniotic injections on gestational day 17 (E17, term = E21-22) of either saline (n = 15) or a solution of 1 mg/mL of ≥95% homogeneous human SIgA (n = 79). Animals were euthanized daily at E18-E21 for quantification of the IgA component by ELISA at gestational membranes, placenta, and select fetal anatomical sites against saline controls procured at term. Statistical analysis was by Mann-Whitney U-test.

RESULTS

None of the saline-injected animals had detectable human IgA. SIgA-injected fetuses showed human IgA in the stomach aspirate, intestinal wall, lungs, liver, and serum at all time points. IgA levels were significantly higher in the gastric aspirate and in the intestine than in all other sites (p < 0.001 for both), with intestinal levels remaining stable through E18-E21 (p = 0.09-0.62 pairwise). Serum and placental levels were consistently low throughout, reaching near zero levels by E21.

CONCLUSIONS

The chronology of exogenous secretory-IgA kinetics after intra-amniotic injection is suggestive of fetal uptake by ingestion, leading to consistent levels in the gastrointestinal tract. Transamniotic fetal immunotherapy (TRAFIT) with secretory-IgA may become a novel strategy for enhancing early mucosal immunity.

LEVEL OF EVIDENCE

N/A (animal and laboratory study).

TYPE OF STUDY

Animal and laboratory study.

The Role of Gut Dysbiosis in the Loss of Intestinal Immune Cell Functions and Viral Pathogenesis

The gut microbiome plays a critical role in maintaining overall health and immune function. However, dysbiosis, an imbalance in microbiome composition, can have profound effects on various aspects of human health, including susceptibility to viral infections. Despite numerous studies investigating the influence of viral infections on gut microbiome, the impact of gut dysbiosis on viral infection and pathogenesis remains relatively understudied. The clinical variability observed in SARS-CoV-2 and seasonal influenza infections, and the presence of natural HIV suppressors, suggests that host-intrinsic factors, including the gut microbiome, may contribute to viral pathogenesis. The gut microbiome has been shown to influence the host immune system by regulating intestinal homeostasis through interactions with immune cells. This review aims to enhance our understanding of how viral infections perturb the gut microbiome and mucosal immune cells, affecting host susceptibility and response to viral infections. Specifically, we focus on exploring the interactions between gamma delta (γδ) T cells and gut microbes in the context of inflammatory viral pathogenesis and examine studies highlighting the role of the gut microbiome in viral disease outcomes. Furthermore, we discuss emerging evidence and potential future directions for microbiome modulation therapy in the context of viral pathogenesis.

Summary of methodology used in enterotoxigenic Escherichia coli (ETEC) challenge experiments in weanling pigs and quantitative assessment of observed variability

Postweaning diarrhea in pigs is often caused by the F4 or F18 strains of enterotoxigenic Escherichia coli (ETEC). To evaluate interventions for ETEC, experimental infection via a challenge model is critical. Others have reviewed ETEC challenge studies, but there is a lack of explanation for the variability in responses observed. Our objective was to quantitatively summarize the responses and variability among ETEC challenge studies and develop a tool for sample size calculation. The most widely evaluated response criteria across ETEC challenge studies consist of growth performance, fecal consistency, immunoglobulins, pro-inflammatory cytokines, and small intestinal morphology. However, there is variation in the responses seen following ETEC infection as well as the variability within each response criteria. Contributing factors include the type of ETEC studied, dose and timing of inoculation, and the number of replications. Generally, a reduction in average daily gain and average daily feed intake are seen following ETEC challenge as well as a rapid increase in diarrhea. The magnitude of response in growth performance varies, and methodologies used to characterize fecal consistency are not standardized. Likewise, fecal bacterial shedding is a common indicator of ETEC infection, but the responses seen across the literature are not consistent due to differences in bacterial enumeration procedures. Emphasis should also be placed on the piglet's immune response to ETEC, which is commonly assessed by quantifying levels of immunoglobulins and pro-inflammatory cytokines. Again, there is variability in these responses across published work due to differences in the timing of sample collection, dose of ETEC pigs are challenged with, and laboratory practices. Small intestinal morphology is drastically altered following infection with ETEC and appears to be a less variable response criterion to evaluate. For each of these outcome variables, we have provided quantitative estimates of the responses seen across the literature as well as the variability within them. While there is a large degree of variability across ETEC challenge experiments, we have provided a quantitative summary of these studies and a Microsoft Excel-based tool was created to calculate sample sizes for future studies that can aid researchers in designing future work.

Formulation Studies to Develop Low-Cost, Orally-Delivered Secretory IgA Monoclonal Antibodies for Passive Immunization Against Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a common cause for diarrheal infections in children in low- and middle-income countries (LMICs). To date, no ETEC vaccine candidates have been approved. Passive immunization with low-cost, oral formulations of secretory IgA (sIgA) against ETEC is an alternative approach to protect high-risk populations in LMICs. Using a model sIgA monoclonal antibody (anti-LT sIgA2-mAb), the stability profiles of different formulations were assessed during storage and in in vitro digestion models (mimicking in vivo oral delivery). First, by employing various physicochemical techniques and a LT-antigen binding assay, three formulations with varying acid-neutralizing capacity (ANC) were evaluated to stabilize sIgA2-mAb during stress studies (freeze-thaw, agitation, elevated temperature) and during exposure to gastric phase digestion. Next, a low-volume, in vitro intestinal digestion model was developed to screen various additives to stabilize sIgA2-mAb in the intestinal phase. Finally, combinations of high ANC buffers and decoy proteins were assessed to collectively protect sIgA2-mAb during in vitro sequential (stomach to intestine) digestion. Based on the results, we demonstrate the feasibility of low-cost, 'single-vial', liquid formulations of sIgA-mAbs delivered orally after infant feeding for passive immunization, and we suggest future work based on a combination of in vitro and in vivo stability considerations.

Defining the Relationship of Gut Microbiota, Immunity, and Cognition in Early Life-A Narrative Review

Recently, the immune system has been identified as one of the possible main bridges which connect the gut-brain axis. This review aims to examine available evidence on the microbiota-immunity-cognitive relationship and its possible effects on human health early in life. This review was assembled by compiling and analyzing various literature and publications that document the gut microbiota-immune system-cognition interaction and its implications in the pediatric population. This review shows that the gut microbiota is a pivotal component of gut physiology, with its development being influenced by a variety of factors and, in return, supports the development of overall health. Findings from current research focus on the complex relationship between the central nervous system, gut (along with gut microbiota), and immune cells, highlighting the importance of maintaining a balanced interaction among these systems for preserving homeostasis, and demonstrating the influence of gut microbes on neurogenesis, myelin formation, the potential for dysbiosis, and alterations in immune and cognitive functions. While limited, evidence shows how gut microbiota affects innate and adaptive immunity as well as cognition (through HPA axis, metabolites, vagal nerve, neurotransmitter, and myelination).

Flagellar-based motility accelerates IgA-mediated agglutination of Salmonella Typhimurium at high bacterial cell densities

Introduction

Secretory IgA (SIgA) protects the intestinal epithelium from enteric pathogens such as Salmonella enterica serovar Typhimurium (STm) through a process known as immune exclusion, where invading bacteria are aggregated via antibody cross-linking, encased in mucus, and then cleared from the intestinal tract via peristalsis. At high cell densities, the STm aggregates form a tightly packed network that is reminiscent of early bacterial biofilms. However, the underlying mechanism of how SIgA mediates this transition from a motile and invasive state to an avirulent sessile state in STm is currently unknown.

Methods

In this report, we developed and validated a methodology known as the "snow globe" assay to enable real-time imaging and quantification of STm agglutination by the mouse monoclonal IgA Sal4.

Results

We observed that agglutination in the snow globe assay was dose-dependent, antigen-specific, and influenced by antibody isotype. We determined that flagellar-based motility was a prerequisite for rapid onset of agglutination, even at high cell densities where cell-cell contacts are expected to be frequent. We also investigated the roles of individual cyclic-di-GMP metabolizing enzymes previously implicated in motility and biofilm formation in Sal4 IgA-mediated agglutination.

Discussion

Taken together, our results demonstrate that IgA-mediated agglutination is a dynamic process influenced by bacterial motility and cell-cell collisions. We conclude that the snow globe assay is a viable platform to further decipher the molecular and genetic determinants that drive this interaction.

Intracellular immunoglobulin A (icIgA) in protective immunity and vaccines

Virus neutralization at respiratory mucosal surfaces is important in the prevention of infection. Mucosal immunity is mediated mainly by extracellular secretory immunoglobulin A (sIgA) and its role has been well studied. However, the protective role of intracellular specific IgA (icIgA) is less well defined. Initially, in vitro studies using epithelial cell lines with surface expressed polymeric immunoglobulin receptor (pIgR) in transwell culture chambers have shown that icIgA can neutralize influenza, parainfluenza, HIV, rotavirus and measles viruses. This effect appears to involve an interaction between polymeric immunoglobulin A (pIgA) and viral particles within an intracellular compartment, since IgA is transported across the polarized cell. Co-localization of specific icIgA with influenza virus in patients' (virus culture positive) respiratory epithelial cells using well-characterized antisera was initially reported in 2018. This review provides a summary of in vitro studies with icIgA on colocalization and neutralization of the above five viruses. Two other highly significant respiratory infectious agents with severe global impacts viz. SARS-2 virus (CoViD pandemic) and the intracellular bacterium-Mycobacterium tuberculosis-are discussed. Further studies will provide more detailed understanding of the mechanisms and kinetics of icIgA neutralization in relation to viral entry and early replication steps with a specific focus on mucosal infections. This will inform the design of more effective vaccines against infectious agents transmitted via the mucosal route.

Carotenoids and Their Health Benefits as Derived via Their Interactions with Gut Microbiota

Carotenoids have been related to a number of health benefits. Their dietary intake and circulating levels have been associated with a reduced incidence of obesity, diabetes, certain types of cancer, and even lower total mortality. Their potential interaction with the gut microbiota (GM) has been generally overlooked but may be of relevance, as carotenoids largely bypass absorption in the small intestine and are passed on to the colon, where they appear to be in part degraded into unknown metabolites. These may include apo-carotenoids that may have biological effects because of higher aqueous solubility and higher electrophilicity that could better target transcription factors, i.e., NF-κB, PPARγ, and RAR/RXRs. If absorbed in the colon, they could have both local and systemic effects. Certain microbes that may be supplemented were also reported to produce carotenoids in the colon. Although some bactericidal aspects of carotenoids have been shown in vitro, a few studies have also demonstrated a prebiotic-like effect, resulting in bacterial shifts with health-associated properties. Also, stimulation of IgA could play a role in this respect. Carotenoids may further contribute to mucosal and gut barrier health, such as stabilizing tight junctions. This review highlights potential gut-related health-beneficial effects of carotenoids and emphasizes the current research gaps regarding carotenoid-GM interactions.

Effects of dietary sulfur amino acid levels on growth performance and intestinal immunity in broilers vaccinated and subsequently infected with coccidiosis

Coccidia vaccination is a common practice in the poultry industry. However, research is lacking regarding the optimal nutritional support for coccidia vaccinated broilers. In this study, broilers were vaccinated with coccidia oocyst at hatch and were fed with a common starter diet from 1 to 10 d. On d 11, the broilers were randomly assigned to groups in a 4 × 2 factorial arrangement. Briefly, the broilers were fed one of four diets containing 0.6, 0.8, 0.9, and 1.0% of standardized ileal digestible methionine plus cysteine (SID M+C), respectively, from 11 to 21 d. On d 14, the broilers from each diet group were orally gavaged with either PBS (Mock challenge) or Eimeria oocysts. Compared to PBS-gavaged broilers and regardless of dietary SID M+C levels, the Eimeria-gavaged broilers had 1) decreased gain-to-feed ratio (15-21 d, P = 0.002; 11-21 d, P = 0.011); 2) increased fecal oocysts (P < 0.001); 3) increased plasma anti-Eimeria IgY (P = 0.033); and 4) increased intestinal luminal interleukin-10 (IL-10; duodenum, P = 0.039; jejunum, P = 0.018) and gamma interferon (IFN-γ; duodenum, P < 0.001; jejunum, P = 0.017). Regardless of Eimeria gavage, broilers fed 0.6% SID M+C had decreased (P<0.001) body weight gain (15-21 and 11-21 d) and gain-to-feed ratio (11-14, 15-21, and 11-21 d) when compared to those fed ≥ 0.8% SID M+C. Eimeria challenge increased (P < 0.001) duodenum lesions when the broilers were fed with 0.6, 0.8, and 1.0% SID M+C, and increased (P = 0.014) mid-intestine lesions when the broilers were fed with 0.6 and 1.0% SID M+C. An interaction between the two experimental factors was detected on plasma anti-Eimeria IgY titers (P = 0.022), as coccidiosis challenge increased plasma anti-Eimeria IgY titers only when the broilers were fed with 0.9% SID M+C. In summary, the dietary SID M+C requirement for grower (11-21 d) broilers vaccinated with coccidiosis was ranged from 0.8 to 1.0% for optimal growth performance and intestinal immunity, regardless of coccidiosis challenge.

When secretion turns into excretion - the different roles of IgA

IgA deficiency is the commonest immunodeficiency affecting up to 1 in 700 individuals. The effects of IgA deficiency are difficult to see in many individuals, are mild in many fewer and severe in fewer still. While monovalent IgA is found in serum, dimeric IgA is secreted through mucosal surfaces where it helps to maintain epithelial homeostasis. Studies with knockout mice have taught us that there are subtle inflammatory consequences of removing secretory IgA (sIgA), and the best explanation for these changes can be related by the loss of the 'excretory' immune system. The excretion of antigens is a logical process in regulating the immune system, given the long half-life of complement fixing antibodies. But the function of IgA as an immune or inflammation regulator may go beyond antigen removal.

Pyruvate: Ferredoxin oxidoreductase is involved in IgA-related microbiota dysbiosis and intestinal inflammation

Introduction

Inflammatory bowel diseases (IBDs) are associated with both immune abnormalities and dysbiosis, characterized by a loss of Faecalibacterium prausnitzii (F. prausnitzii). However, the reason for F. prausnitzii deficiency remains unclear.

Methods

16S rDNA seque-ncing and IgA enzyme-linked immunosorbent assay (ELISA) were applied to identify bacterial community and IgA changes in ulcerative colitis (UC) patients. Forced immunization with F. prausnitzii in rabbits was conducted. To screen for potential IgA-reactive proteins in F. prausnitzii lysates, we performed western blotting and mass spectrometry analyses. Pyruvate: ferredoxin oxidoreductase (PFOR) was cloned and purified, then the immunoreactivity of PFOR was verified in peripheral blood mononuclear cells (PBMCs) through PCR, ELISpot assay and single-cell sequencing (scRNA-seq). Finally, the UC fecal dysbiosis was re-analyzed in the context of the phylogenetic tree of PFOR.

Results

F. prausnitzii was underrepresented in UC patients with elevated F. prausnitzii-reactive IgA in the fecal supernatant. Forced immunization with F. prausnitzii in rabbits led to high interferon-γ (IFN-γ) transcription in the colon, along with beta diversity disturbance and intestinal inflammation. PFOR was identified as an IgA-binding antigen of F. prausnitzii and the immunoreactivity was validated in PBMCs, which showed elevated expression of inflammatory cytokines. The scRNA-seq revealed enhanced signals in both T regulatory cells (Tregs) and monocytes after PFOR incubation. Furthermore, phylogenetic analysis revealed that PFOR was a common but conserved protein among the gut bacteria.

Discussion

Our results collectively suggest that PFOR is a bioactive protein in the immune system and may contribute to host-microbial crosstalk. Conserved but bioactive microbial proteins, such as PFOR, warrant more attention in future host-microbial interaction studies.

Protective immunity enhanced Salmonella vaccine vectors delivering Helicobacter pylori antigens reduce H. pylori stomach colonization in mice

Helicobacter pylori is a major cause of gastric mucosal inflammation, peptic ulcers, and gastric cancer. Emerging antimicrobial-resistant H. pylori has hampered the effective eradication of frequent chronic infections. Moreover, a safe vaccine is highly demanded due to the absence of effective vaccines against H. pylori. In this study, we employed a new innovative Protective Immunity Enhanced Salmonella Vaccine (PIESV) vector strain to deliver and express multiple H. pylori antigen genes. Immunization of mice with our vaccine delivering the HpaA, Hp-NAP, UreA and UreB antigens, provided sterile protection against H. pylori SS1 infection in 7 out of 10 tested mice. In comparison to the control groups that had received PBS or a PIESV carrying an empty vector, immunized mice exhibited specific and significant cellular recall responses and antigen-specific serum IgG1, IgG2c, total IgG and gastric IgA antibody titers. In conclusion, an improved S. Typhimurium-based live vaccine delivering four antigens shows promise as a safe and effective vaccine against H. pylori infection.

Interactions of Microbiota and Mucosal Immunity in the Ceca of Broiler Chickens Infected with Eimeria tenella

The purpose of the study was to investigate the effects of Eimeria tenella infection on the cecal microbiome, the protein concentration of cecal content, cecal mucosal immunity, and serum endotoxin levels in broilers. Three hundred sixty 14-day-old broilers were allocated to five infection doses with six replicates. The five infection doses were: ID0: 0, ID1: 6250, ID2: 12,500, ID3: 25,000, and ID4: 50,000 Eimeria tenella oocysts. Eimeria tenella infection significantly increased the relative abundance of the phylum Proteobacteria, which includes diverse pathogenic bacteria, and significantly decreased the relative abundance of the phylum Firmicutes. Protein concentration of the cecal content was linearly increased (p < 0.05), and the concentration of secretory immunoglobulin A (sIgA) in the cecal content was linearly decreased by Eimeria tenella infection (p < 0.05). Goblet cell density was linearly reduced in the ceca by Eimeria tenella infection (p < 0.05). Eimeria tenella infection tended to linearly decrease the relative mRNA expression of antimicrobial peptide genes such as avian beta-defensin 9 (AvBD9; p = 0.10) and liver-expressed antimicrobial peptide 2 (LEAP2; p = 0.08) in the cecal tissue. Therefore, Eimeria tenella infection negatively modulated cecal microbiota via impairing cecal mucosal immunity and increasing protein concentration in the cecal content in broilers.

An intranasal vaccine targeting the receptor binding domain of SARS-CoV-2 elicits a protective immune response

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pathogen responsible for COVID-19, has caused an ongoing worldwide pandemic. Due to the rapid emergence of variants of concern (VOCs), novel vaccines and vaccination strategies are urgently needed. We developed an intranasal vaccine consisting of the SARS-CoV-2 receptor binding domain (RBD) fused to the antibody Fc fragment (RBD-Fc). RBD-Fc could induce strong humoral immune responses via intranasal vaccination. Notably, this immunogen could efficiently induce IgG and IgA and establish mucosal immunity in the respiratory tract. The induced antibodies could efficiently neutralize wild-type SARS-CoV-2 and currently identified SARS-CoV-2 VOCs, including the Omicron variant. In a mouse model, intranasal immunization could provide complete protection against a lethal SARS-CoV-2 challenge. Unfortunately, the limitation of our study is the small number of animals used in the immune response analysis. Our results suggest that recombinant RBD-Fc delivered via intranasal vaccination has considerable potential as a mucosal vaccine that may reduce the risk of SARS-CoV-2 infection.

Harnessing Nasal Immunity with IgA to Prevent Respiratory Infections

The nasal cavity is a primary checkpoint for the invasion of respiratory pathogens. Numerous pathogens, including SARS-CoV-2, S. pneumoniae, S. aureus, etc., can adhere/colonize nasal lining to trigger an infection. Secretory IgA (sIgA) serves as the first line of immune defense against foreign pathogens. sIgA facilitates clearance of pathogenic microbes by intercepting their access to epithelial receptors and mucus entrapment through immune exclusion. Elevated levels of neutralizing IgA at the mucosal surfaces are associated with a high level of protection following intranasal immunizations. This review summarizes recent advances in intranasal vaccination technology and challenges in maintaining nominal IgA levels at the mucosal surface. Overall, the review emphasizes the significance of IgA-mediated nasal immunity, which holds a tremendous potential to mount protection against respiratory pathogens.

A Dual Adjuvant System for Intranasal Boosting of Local and Systemic Immunity for Influenza Vaccination

Systemically vaccinated individuals against COVID-19 and influenza may continue to support viral replication and shedding in the upper airways, contributing to the spread of infections. Thus, a vaccine regimen that enhances mucosal immunity in the respiratory mucosa is needed to prevent a pandemic. Intranasal/pulmonary (IN) vaccines can promote mucosal immunity by promoting IgA secretion at the infection site. Here, we demonstrate that an intramuscular (IM) priming-IN boosting regimen with an inactivated influenza A virus adjuvanted with the liposomal dual TLR4/7 adjuvant (Fos47) enhances systemic and local/mucosal immunity. The IN boosting with Fos47 (IN-Fos47) enhanced antigen-specific IgA secretion in the upper and lower respiratory tracts compared to the IM boosting with Fos47 (IM-Fos47). The secreted IgA induced by IN-Fos47 was also cross-reactive to multiple influenza virus strains. Antigen-specific tissue-resident memory T cells in the lung were increased after IN boosting with Fos47, indicating that IN-Fos47 established tissue-resident T cells. Furthermore, IN-Fos47 induced systemic cross-reactive IgG antibody titers comparable to those of IM-Fos47. Neither local nor systemic reactogenicity or adverse effects were observed after IN delivery of Fos47. Collectively, these results indicate that the IM/IN regimen with Fos47 is safe and provides both local and systemic anti-influenza immune responses.

Development of Nasal Vaccines and the Associated Challenges

Viruses, bacteria, fungi, and several other pathogenic microorganisms usually infect the host via the surface cells of respiratory mucosa. Nasal vaccination could provide a strong mucosal and systemic immunity to combat these infections. The intranasal route of vaccination offers the advantage of easy accessibility over the injection administration. Therefore, nasal immunization is considered a promising strategy for disease prevention, particularly in the case of infectious diseases of the respiratory system. The development of a nasal vaccine, particularly the strategies of adjuvant and antigens design and optimization, enabling rapid induction of protective mucosal and systemic responses against the disease. In recent times, the development of efficacious nasal vaccines with an adequate safety profile has progressed rapidly, with effective handling and overcoming of the challenges encountered during the process. In this context, the present report summarizes the most recent findings regarding the strategies used for developing nasal vaccines as an efficient alternative to conventional vaccines.

Agglutination of Borreliella burgdorferi by Transmission-Blocking OspA Monoclonal Antibodies and Monovalent Fab Fragments

Lyme disease vaccines based on recombinant Outer surface protein A (OspA) elicit protective antibodies that interfere with tick-to-host transmission of the disease-causing spirochete Borreliella burgdorferi. Another hallmark of OspA antisera and certain OspA monoclonal antibodies (MAbs) is their capacity to induce B. burgdorferi agglutination in vitro, a phenomenon first reported more than 30 years ago but never studied in molecular detail. In this report, we demonstrate that transmission-blocking OspA MAbs, individually and in combination, promote dose-dependent and epitope-specific agglutination of B. burgdorferi. Agglutination occurred within minutes and persisted for hours. Spirochetes in the core of the aggregates exhibited evidence of outer membrane (OM) stress, revealed by propidium iodide uptake. The most potent agglutinator was the mouse MAb LA-2, which targets the OspA C terminus (β-strands 18 to 20). Human MAb 319-44, which also targets the OspA C terminus (β-strand 20), and 857-2, which targets the OspA central β-sheet (strands 8 to 10), were less potent agglutinators, while MAb 221-7, which targets β-strands 10 to 11, had little to no measurable agglutinating activity, even though its affinity for OspA exceeded that of LA-2. Remarkably, monovalent Fab fragments derived from LA-2, and to a lesser degree 319-44, retained the capacity to induce B. burgdorferi aggregation and OM stress, a particularly intriguing observation considering that "LA-2-like" Fabs have been shown to experimentally entrap B. burgdorferi within infected ticks and prevent transmission during feeding to a mammalian host. It is therefore tempting to speculate that B. burgdorferi aggregation triggered by OspA-specific antibodies in vitro may in fact reflect an important biological activity in vivo.

Constitution of mucosa‐associated microbiota in the lower digestive tract does not change in early stage of non‐alcoholic fatty liver disease with fecal dysbiosis

Background and Aim

Methods

Results

Conclusion

Aetiology, diagnosis and management of small intestinal bacterial overgrowth

Small intestinal bacterial overgrowth is a small bowel disorder characterised by excessive amounts of bacteria populating the small intestine leading to symptoms of abdominal pain, bloating and change in bowel habit. This creates some degree of diagnostic uncertainty due to the overlap of these symptoms with numerous other gastrointestinal conditions. Quantitative culture of jejunal aspirates is the gold standard diagnostic test but has largely been replaced by glucose and lactulose breath tests due to their relative ease and accessibility. The approach to treatment centres around reducing bacterial numbers through antibiotic therapy and managing any predisposing factors. Further research is required in order to define the optimum antibiotic choice and duration of therapy as well as the potential diagnostic utility of home breath testing and capsule-based technology.

Passive Immunotherapy Against SARS-CoV-2: From Plasma-Based Therapy to Single Potent Antibodies in the Race to Stay Ahead of the Variants

The COVID-19 pandemic is now approaching 2 years old, with more than 440 million people infected and nearly six million dead worldwide, making it the most significant pandemic since the 1918 influenza pandemic. The severity and significance of SARS-CoV-2 was recognized immediately upon discovery, leading to innumerable companies and institutes designing and generating vaccines and therapeutic antibodies literally as soon as recombinant SARS-CoV-2 spike protein sequence was available. Within months of the pandemic start, several antibodies had been generated, tested, and moved into clinical trials, including Eli Lilly's bamlanivimab and etesevimab, Regeneron's mixture of imdevimab and casirivimab, Vir's sotrovimab, Celltrion's regdanvimab, and Lilly's bebtelovimab. These antibodies all have now received at least Emergency Use Authorizations (EUAs) and some have received full approval in select countries. To date, more than three dozen antibodies or antibody combinations have been forwarded into clinical trials. These antibodies to SARS-CoV-2 all target the receptor-binding domain (RBD), with some blocking the ability of the RBD to bind human ACE2, while others bind core regions of the RBD to modulate spike stability or ability to fuse to host cell membranes. While these antibodies were being discovered and developed, new variants of SARS-CoV-2 have cropped up in real time, altering the antibody landscape on a moving basis. Over the past year, the search has widened to find antibodies capable of neutralizing the wide array of variants that have arisen, including Alpha, Beta, Gamma, Delta, and Omicron. The recent rise and dominance of the Omicron family of variants, including the rather disparate BA.1 and BA.2 variants, demonstrate the need to continue to find new approaches to neutralize the rapidly evolving SARS-CoV-2 virus. This review highlights both convalescent plasma- and polyclonal antibody-based approaches as well as the top approximately 50 antibodies to SARS-CoV-2, their epitopes, their ability to bind to SARS-CoV-2 variants, and how they are delivered. New approaches to antibody constructs, including single domain antibodies, bispecific antibodies, IgA- and IgM-based antibodies, and modified ACE2-Fc fusion proteins, are also described. Finally, antibodies being developed for palliative care of COVID-19 disease, including the ramifications of cytokine release syndrome (CRS) and acute respiratory distress syndrome (ARDS), are described.

Dealing with a mucosal viral pandemic: lessons from COVID-19 vaccines

The development and deployment of vaccines against COVID-19 demonstrated major successes in providing immunity and preventing severe disease and death. Yet SARS-CoV-2 evolves and vaccine-induced protection wanes, meaning progress in vaccination strategies is of upmost importance. New vaccines directed at emerging viral strains are being developed while vaccination schemes with booster doses and combinations of different platform-based vaccines are being tested in trials and real-world settings. Despite these diverse approaches, COVID-19 vaccines are only delivered intramuscularly, whereas the nasal mucosa is the primary site of infection with SARS-CoV-2. Preclinical mucosal vaccines with intranasal or oral administration demonstrate promising results regarding mucosal IgA generation and tissue-resident lymphocyte responses against SARS-CoV-2. By mounting an improved local humoral and cell-mediated response, mucosal vaccination could be a safe and effective way to prevent infection, block transmission and contribute to reduce SARS-CoV-2 spread. However, questions and limitations remain: how effectively and reproducibly will vaccines penetrate mucosal barriers? Will vaccine-induced mucosal IgA responses provide sustained protection against infection?

Bruton's Tyrosine Kinase Supports Gut Mucosal Immunity and Commensal Microbiome Recognition in Autoimmune Arthritis

Bruton's tyrosine kinase (Btk) deficiency preferentially eliminates autoreactive B cells while sparing normal humoral responses, but has not been studied in mucosal immunity. Commensal microbes and intact BTK signaling have been independently shown to be essential for arthritis development in K/BxN mice. Here, we examine how BTK-mediated signaling interfaces with the gut microbiome. Btk-deficient K/BxN mice were found to have small Peyer's Patches with reduced germinal center and IgA class-switched B cells. IgA-switched plasma cells in small intestines were reduced, especially in villi of Btk-deficient mice. IgH CDR3 sequencing showed similar V gene diversity and somatic hypermutation frequency despite Btk deficiency but showed reduced CDR3 amino acid polarity, suggesting potential qualitative differences in the gut plasma cell repertoire. Small intestinal IgA was low and IgA coating of commensal bacteria was reduced. IgA-seq showed a shift in small intestinal microbes that are normally IgA-coated into the uncoated fraction in Btk-deficient mice. Overall, this study shows that BTK supports normal intestinal IgA development in response to commensals. This manuscript was previously published as a preprint at: https://www.biorxiv.org/content/10.1101/2021.03.10.434762v2.

The Role of IgA in Chronic Upper Airway Disease: Friend or Foe?

Chronic upper airway inflammation is amongst the most prevalent chronic disease entities in the Western world with prevalence around 30% (rhinitis) and 11% (rhinosinusitis). Chronic rhinitis and rhinosinusitis may severely impair the quality of life, leading to a significant socio-economic burden. It becomes more and more clear that the respiratory mucosa which forms a physiological as well as chemical barrier for inhaled particles, plays a key role in maintaining homeostasis and driving disease. In a healthy state, the mucosal immune system provides protection against pathogens as well as maintains a tolerance toward non-harmful commensal microbes and benign environmental substances such as allergens. One of the most important players of the mucosal immune system is immunoglobulin (Ig) A, which is well-studied in gut research where it has emerged as a key factor in creating tolerance to potential food allergens and maintaining a healthy microbiome. Although, it is very likely that IgA plays a similar role at the level of the respiratory epithelium, very little research has been performed on the role of this protein in the airways, especially in chronic upper airway diseases. This review summarizes what is known about IgA in upper airway homeostasis, as well as in rhinitis and rhinosinusitis, including current and possible new treatments that may interfere with the IgA system. By doing so, we identify unmet needs in exploring the different roles of IgA in the upper airways required to find new biomarkers or therapeutic options for treating chronic rhinitis and rhinosinusitis.

Cutting Edge: Serum but Not Mucosal Antibody Responses Are Associated with Pre-Existing SARS-CoV-2 Spike Cross-Reactive CD4+ T Cells following BNT162b2 Vaccination in the Elderly

Advanced age is a main risk factor for severe COVID-19. However, low vaccination efficacy and accelerated waning immunity have been reported in this age group. To elucidate age-related differences in immunogenicity, we analyzed human cellular, serological, and salivary SARS-CoV-2 spike glycoprotein-specific immune responses to the BNT162b2 COVID-19 vaccine in old (69-92 y) and middle-aged (24-57 y) vaccinees compared with natural infection (COVID-19 convalescents, 21-55 y of age). Serological humoral responses to vaccination excee-ded those of convalescents, but salivary anti-spike subunit 1 (S1) IgA and neutralizing capacity were less durable in vaccinees. In old vaccinees, we observed that pre-existing spike-specific CD4⁺ T cells are associated with efficient induction of anti-S1 IgG and neutralizing capacity in serum but not saliva. Our results suggest pre-existing SARS-CoV-2 cross-reactive CD4⁺ T cells as a predictor of an efficient COVID-19 vaccine-induced humoral immune response in old individuals.

Dietary regulation of the SIgA-gut microbiota interaction

Gut microbiota (GM) is essential for host health, and changes in the GM are related to the development of various diseases. Recently, secretory immunoglobulin A (SIgA), the most abundant immunoglobulin isotype in the intestinal mucosa, has been found to play an essential role in controlling GM. SIgA dysfunction can lead to changes in the GM and is associated with the development of various GM-related diseases. Although in early stage, recent studies have shown that assorted dietary interventions, including vitamins, amino acids, fatty acids, polyphenols, oligo/polysaccharides, and probiotics, can influence the intestinal SIgA response and SIgA-GM interaction. Dietary intervention can enhance the SIgA response by directly regulating it (from top to bottom) or by regulating the GM structure or gene expression (from bottom to top). Furthermore, intensive studies involving the particular influence of dietary intervention on SIgA-binding to the GM and SIgA repertoire and the precise regulation of the SIgA response via dietary intervention are still exceedingly scarce and merit further consideration. This review summarizes the existing knowledge and (possible) mechanisms of the influence of dietary intervention on the SIgA-GM interaction. Key issues are considered, and the approaches in addressing these issues in future studies are also discussed.

Sculpting therapeutic monoclonal antibody N-glycans using endoglycosidases

Immunoglobulin G (IgG) monoclonal antibodies are a prominent and expanding class of therapeutics used for the treatment of diverse human disorders. The chemical composition of the N-glycan on the fragment crystallizable (Fc) region determines the effector functions through interaction with the Fc gamma receptors and complement proteins. The chemoenzymatic synthesis using endo-β-N-acetylglucosaminidases (ENGases) emerged as a strategy to obtain antibodies with customized glycoforms that modulate their therapeutic activity. We discuss the molecular mechanism by which ENGases recognize different N-glycans and protein substrates, especially those that are specific for IgG antibodies, in order to rationalize the glycoengineering of immunotherapeutic antibodies, which increase the impact on the treatment of myriad diseases.

Salmonella Uptake into Gut-Associated Lymphoid Tissues: Implications for Targeted Mucosal Vaccine Design and Delivery

Peyer's patches are organized gut-associated lymphoid tissues (GALT) in the small intestine and the primary route by which particulate antigens, including viruses and bacteria, are sampled by the mucosal immune system. Antigen sampling occurs through M cells, a specialized epithelial cell type located in the follicle-associated epithelium (FAE) that overlie Peyer's patch lymphoid follicles. While Peyer's patches play an integral role in intestinal homeostasis, they are also a gateway by which enteric pathogens, like Salmonella enterica serovar Typhimurium (STm), cross the intestinal barrier. Once pathogens like STm gain access to the underlying network of mucosal dendritic cells and macrophages they can spread systemically. Thus, Peyer's patches are at the crossroads of mucosal immunity and intestinal pathogenesis. In this chapter, we provide detailed methods to assess STm entry into mouse Peyer's patch tissues. We describe Peyer's patch collection methods and provide strategies to enumerate bacterial uptake. We also detail a method for quantifying bacterial shedding from infected animals and provide an immunohistochemistry protocol for the localization of STm along the gastrointestinal tract and insight into pathogen transit in the presence of protective antibodies. While the protocols are written for STm, they are easily tailored to other enteric pathogens.

Beware of Mycoplasma Anti-immunoglobulin Strategies

Mycoplasmas are small, genome-reduced bacteria. They are obligate parasites that can be found in a wide range of host species, including the majority of livestock animals and humans. Colonization of the host can result in a wide spectrum of outcomes. In many cases, these successful parasites are considered commensal, as they are found in the microbiota of asymptomatic carriers. Conversely, mycoplasmas can also be pathogenic, as they are associated with a range of both acute and chronic inflammatory diseases which are problematic in veterinary and human medicine. The chronicity of mycoplasma infections and the ability of these bacteria to infect even recently vaccinated individuals clearly indicate that they are able to successfully evade their host’s humoral immune response. Over the years, multiple strategies of immune evasion have been identified in mycoplasmas, with a number of them aimed at generating important antigenic diversity. More recently, mycoplasma-specific anti-immunoglobulin strategies have also been characterized. Through the expression of the immunoglobulin-binding proteins protein M or mycoplasma immunoglobulin binding (MIB), mycoplasmas have the ability to target the host’s antibodies and to prevent them from interacting with their cognate antigens. In this review, we discuss how these discoveries shed new light on the relationship between mycoplasmas and their host’s immune system. We also propose that these strategies should be taken into consideration for future studies, as they are key to our understanding of mycoplasma diseases' chronic and inflammatory nature and are probably a contributing factor to reduce vaccine efficacy.

Induced Polyspecificity of Human Secretory Immunoglobulin A Antibodies: Is It Possible to Improve Their Ability to Bind Pathogens?

INTRODUCTION

As has been shown previously, various protein-modifying agents can change the antigen-binding properties of immunoglobulins. However, induced polyspecificity of human secretory immunoglobulin A (sIgA) has not been previously characterized in detail.

METHODS

In the present study, human secretory immunoglobulin A (IgA) was exposed to buffers with acidic pH, to free heme, or to pro-oxidative ferrous ions, and the antigen-binding behavior of the native and modified IgA to viral and bacterial antigens was compared using Western blotting and enzyme-linked immunosorbent assay. The ability of these agents to modulate the antigen-binding properties of human sIgA toward a wide range of pathogen peptides was investigated using an epitope microarray.

RESULTS

We have shown that acidic pH, heme, and pro-oxidative ferrous ions influenced the binding of secretory IgA in opposite directions (either increasing or decreasing); however, the strongest effect was observed when using buffers with low pH. This fraction had the highest number of affected reactivities; most of them were increased and most of the new ones were toward common pathogens.

CONCLUSIONS

Thus, it was shown that all investigated treatments can alter to some degree the antigen-binding of secretory IgA, but acidic pH has the most potentially beneficial effect by increasing binding to a largest number of common pathogens' antigens.

Affinity-based clonal selection in Peyer's patches

Effective long-lasting immunity depends on the generation of protective antibodies that restrict the invasion of harmful pathogens. The germinal center (GC) is a microanatomical site at which B cells acquire random somatic mutations in their immunoglobulin genes followed by affinity-based selection. Whereas this process was extensively studied in lymph nodes and spleen, less is known about GCs located in mucosal tissues lymphoid organs, such as the Peyer's patches (PPs). These lymphoid organs have a special structure and host a unique niche known as the subepithelial dome (SED), where B cell activation and class switch recombination to IgA take place before GC seeding. As opposed to typical lymph-nodes, the PPs host chronic GC reactions that are driven by gut-bacteria. Direct evidence for antibody affinity maturation in PPs, and competition between B cells for T cell help was recently obtained. Here, we discuss these findings and how they complement each other.

Responsiveness of fecal immunoglobulin A to HPA-axis activation limits its use for mucosal immunity assessment

The assessment of mucosal immunity as a component of animal health is an important aspect for the understanding of variation in host immunity, and its tradeoff against other life-history traits. We investigated immunoglobulin A (IgA), the major type of antibody associated with mucosal immunity, in relation to changes in parasitic burden following anthelminthic treatment in noninvasively collected fecal samples in a semi-free ranging group of Barbary macaques (Macaca sylvanus). We measured IgA in 340 fecal samples of fourteen females and nine males. As IgA has been found to be responsive to stressors, we also related fecal IgA (fIgA) levels to fecal glucocorticoid metabolites (fGCM) measured in the same samples as part of a previous study. We found a high variability within and between individual fIgA levels over time. Running generalized additive mixed models, we found that fIgA levels were higher in males than in females, but did not change in response to the anthelmintic treatment and the resulting reduction in worm burden. Instead, fIgA level changes were significantly correlated to changes in fGCM levels. Our findings indicate that due to the strong responsiveness of fIgA to HPA-axis activity, the measurement of fIgA may have certain limitations with respect to reflecting gastrointestinal parasitic burden. Moreover, the responsiveness of fIgA to stressors interferes with the interpretation of IgA levels in fecal samples as a measure of mucosal immunity, at least in our study population of the Barbary macaques.

The gut microbiota induces Peyer's-patch-dependent secretion of maternal IgA into milk

The evolutionary strategy of transferring maternal antibodies via milk profoundly impacts the survival, lifelong health, and wellbeing of all neonates, including a pronounced impact on human breastfeeding success and infant development. While there has been increased recognition that interorgan connectivity influences the quality of a mother's milk, potentially to personalize it for her offspring, the underlying bases for these processes are incompletely resolved. Here, we define an essential role of Peyer's patches (PPs) for the generation of plasma cells that secrete maternal immunoglobulin A (IgA) into milk. Our metagenomic analysis reveals that the presence of certain residential microorganisms in the gastrointestinal (GI) tract, such as Bacteroides acidifaciens and Prevotella buccalis, is indispensable for the programming of maternal IgA synthesis prior to lactational transfer. Our data provide important insights into how the microbiome of the maternal GI environment, specifically through PPs, can be communicated to the next generation via milk.

Inhaled vaccine delivery in the combat against respiratory viruses: a 2021 overview of recent developments and implications for COVID-19

INTRODUCTION

As underlined by the late 2019 outbreak of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), vaccination remains the cornerstone of global health-care. Although vaccines for SARS-CoV-2 are being developed at a record-breaking pace, the majority of those that are licensed or currently registered in clinical trials are formulated as an injectable product, requiring a tightly regulated cold-chain infrastructure, and primarily inducing systemic immune responses.

AREAS COVERED

Here, we shed light on the status of inhaled vaccines against viral pathogens, providing background to the role of the mucosal immune system and elucidating what factors determine an inhalable vaccine's efficacy. We also discuss whether the development of an inhalable powder vaccine formulation against SARS-CoV-2 could be feasible. The review was conducted using relevant studies from PubMed, Web of Science and Google Scholar.

EXPERT OPINION

We believe that the scope of vaccine research should be broadened toward inhalable dry powder formulations since dry vaccines bear several advantages. Firstly, their dry state can tremendously increase vaccine stability and shelf-life. Secondly, they can be inhaled using disposable inhalers, omitting the need for trained health-care personnel and, therefore, facilitating mass-vaccination campaigns. Thirdly, inhalable vaccines may provide improved protection since they can induce an IgA-mediated mucosal immune response.

Tolerogenic Immunoregulation towards Salmonella Enteritidis Contributes to Colonization Persistence in Young Chicks

Long-term survival and the persistence of bacteria in the host suggest either host unresponsiveness or induction of an immunological tolerant response to the pathogen. The role of the host immunological response to persistent colonization of Salmonella Enteritidis (SE) in chickens remains poorly understood. In the current study, we performed a cecal tonsil transcriptome analysis in a model of SE persistent infection in 2-week-old chickens to comprehensively examine the dynamics of host immunological responses in the chicken gastrointestinal tract. Our results revealed overall host tolerogenic adaptive immune regulation in a major gut-associated lymphoid tissue, the cecal tonsil, during SE infection. Specifically, we observed consistent downregulation of the metallothionein 4 gene at all four postinfection time points (3, 7, 14, and 21 days postinfection [dpi]), which suggested potential pathogen-associated manipulation of the host zinc regulation as well as a possible immune modulatory effect. Furthermore, delayed activation in the B cell receptor signaling pathway and failure to sustain its active state during the lag phase of infection were further supported by an insignificant production of both intestinal and circulatory antibodies. Tug-of-war for interleukin 2 (IL-2) regulation between effector T cells and regulatory T cells appears to have consequences for upregulation in the transducer of ERBB2 (TOB) pathway, a negative regulator of T cell proliferation. In conclusion, this work highlights the overall host tolerogenic immune response that promotes persistent colonization by SE in young layer chicks.

Recombinant Human Secretory IgA Induces Salmonella Typhimurium Agglutination and Limits Bacterial Invasion into Gut-Associated Lymphoid Tissues

As the predominant antibody type in mucosal secretions, human colostrum, and breast milk, secretory IgA (SIgA) plays a central role in safeguarding the intestinal epithelium of newborns from invasive enteric pathogens like the Gram-negative bacterium Salmonella enterica serovar Typhimurium (STm). SIgA is a complex molecule, consisting of an assemblage of two or more IgA monomers, joining (J)-chain, and secretory component (SC), whose exact functions in neutralizing pathogens are only beginning to be elucidated. In this study, we produced and characterized a recombinant human SIgA variant of Sal4, a well-characterized monoclonal antibody (mAb) specific for the O5-antigen of STm lipopolysaccharide (LPS). We demonstrate by flow cytometry, light microscopy, and fluorescence microscopy that Sal4 SIgA promotes the formation of large, densely packed bacterial aggregates in vitro. In a mouse model, passive oral administration of Sal4 SIgA was sufficient to entrap STm within the intestinal lumen and reduce bacterial invasion into gut-associated lymphoid tissues by several orders of magnitude. Bacterial aggregates induced by Sal4 SIgA treatment in the intestinal lumen were recalcitrant to immunohistochemical staining, suggesting the bacteria were encased in a protective capsule. Indeed, a crystal violet staining assay demonstrated that STm secretes an extracellular matrix enriched in cellulose following even short exposures to Sal4 SIgA. Collectively, these results demonstrate that recombinant human SIgA recapitulates key biological activities associated with mucosal immunity and raises the prospect of oral passive immunization to combat enteric diseases.

Traffic generated emissions alter the lung microbiota by promoting the expansion of Proteobacteria in C57Bl/6 mice placed on a high-fat diet

Air pollution has been documented to contribute to severe respiratory diseases like asthma and chronic obstructive pulmonary disorder (COPD). Although these diseases demonstrate a shift in the lung microbiota towards Proteobacteria, the effects of traffic generated emissions on lung microbiota profiles have not been well-characterized. Thus, we investigated the hypothesis that exposure to traffic-generated emissions can alter lung microbiota and immune defenses. Since a large population of the Western world consumes a diet rich in fats, we sought to investigate the synergistic effects of mixed vehicle emissions and high-fat diet consumption. We exposed 3-month-old male C57Bl/6 mice placed either on regular chow (LF) or a high-fat (HF: 45% kcal fat) diet to mixed emissions (ME: 30 µg PM/m³ gasoline engine emissions+70 µg PM/m³ diesel engine emissions) or filtered air (FA) for 6 h/d, 7 d/wk for 30 days. Levels of pulmonary immunoglobulins IgA, IgG, and IgM were analyzed by ELISA, and lung microbial profiling was done using qPCR and Illumina 16 S sequencing. We observed a significant decrease in lung IgA in the ME-exposed animals, compared to the FA-exposed animals, both fed a HF diet. Our results also revealed a significant decrease in lung IgG in the ME-exposed animals both on the LF diet and HF diet, in comparison to the FA-exposed animals. We also observed an expansion of Enterobacteriaceae belonging to the Proteobacteria phylum in the ME-exposed groups on the HF diet. Collectively, we show that the combined effects of ME and HF diet result in decreased immune surveillance and lung bacterial dysbiosis, which is of significance in lung diseases.

Interaction between IgA and gut microbiota and its role in controlling metabolic syndrome

Immunoglobulin A (IgA) is the most abundant immunoglobulin isotype secreted into the mucosal tissues, mainly intestinal mucus. Humans can produce several grams of IgA every day, accounting for three quarters of the body's total immunoglobulin content. IgA, together with mucus and antimicrobial peptides, forms the first line of defence for intestinal epithelial cells, protecting them from a significant number of intestinal antigens. IgA also plays a principal role in controlling the gut microbiota (GM), and disruption in IgA can result in dysbiosis, such as the enrichment of Proteobacteria, which are generally bound by IgA. Proteobacteria overexpansion is also usually seen in obesity and colitis. Consistent with this, IgA dysfunction frequently results in metabolic syndrome (MetS), including conditions such as obesity, adiposity, insulin resistance, and inflammation. In contrast, enhanced IgA function can improve, and even prevent, MetS. Interactions among IgA, GM, and metabolism provide a promising avenue to combat MetS.

Circadian Clock Disruption Suppresses PDL1+ Intraepithelial B Cells in Experimental Colitis and Colitis-Associated Colorectal Cancer

BACKGROUND & AIMS

The circadian clock is crucial for physiological homeostasis including gut homeostasis. Disorder of the circadian clock may contribute to many diseases including inflammatory bowel disease (IBD). However, the role and the mechanisms of circadian clock involvement in IBD still are unclear.

METHODS

Disorder of the circadian clock including chronic social jet lag and circadian clock gene deficiency mice (Bmal1-/-, and Per1-/-Per2-/-) were established. Dextran sulfate sodium (DSS) and/or azoxymethane were used to induce mouse models of colitis and its associated colorectal cancer. Flow cytometry, immunohistochemistry, immunofluorescence, Western blot, and reverse-transcription quantitative polymerase chain reaction were used to analyze the characteristics of immune cells and their related molecules.

RESULTS

Mice with disorders of the circadian clock including chronic social jet lag and circadian clock gene deficiency were susceptible to colitis. Functionally, regulatory B (Breg) cells highly expressing Programmed cell death 1 ligand 1 (PDL1) in intestinal intraepithelial lymphocytes (IELs) helped to alleviate the severity of colitis after DSS treatment and was dysregulated in DSS-treated Bmal1-/- mice. Notably, interleukin 33 in the intestinal microenvironment was key for Bmal1-regulated PDL1+ Breg cells and interleukin 33 was a target of Bmal1 transcriptionally. Dysregulated PDL1+ B cells induced cell death of activated CD4+ T cells in DSS-treated Bmal1-/- mice. Consequently, circadian clock disorder was characterized as decreased numbers of Breg+ PDL1+ cells in IELs and dysfunction of CD4+ T cells promoted colitis-associated colorectal cancer (CRC) in mice. In clinical samples from CRC patients, low expression of Bmal1 gene in paracancerous tissues and center area of tumor was associated closely with a poorer prognosis of CRC patients.

CONCLUSIONS

Our study uncovers the importance of the circadian clock regulating PDL1+ Breg+ cells of IELs in IBD and IBD-associated CRC.

Navy Bean Supplementation in Established High-Fat Diet-Induced Obesity Attenuates the Severity of the Obese Inflammatory Phenotype

Cooked common beans (Phaseolus vulgaris) improve intestinal health in lean mice and attenuate intestinal dysbiosis and inflammation when consumed concurrent with obesity development. We determined the effects of a high-fat (HF) bean supplemented diet in mice with established obesity (induced by 12 weeks of HF diet (60% fat as kcal)) compared to obese mice consuming a HF or low-fat (LF) weight loss control diet. Obese C57BL/6 male mice remained consuming HF for eight weeks or were randomly switched from HF to an isocaloric HF with 15.7% cooked navy bean powder diet (HF→HFB) or LF (11% fat as kcal; HF→LF) (n = 12/group). HF→HFB improved the obese phenotype, including (i) fecal microbiome (increased Prevotella, Akkermansia muciniphila, and short-chain fatty acid levels), (ii) intestinal health (increased ZO-1, claudin-2, Muc2, Relmβ, and Reg3γ expression), and (iii) reduced adipose tissue (AT) inflammatory proteins (NFκBp65, STAT3, IL-6, MCP-1, and MIP-1α), versus HF (p < 0.05). Conversely, HF→LF reduced body weight and circulating hormones (leptin, resistin, and PAI-1) versus HF and HF→HFB (p < 0.05); however, AT inflammation and intestinal health markers were not improved to the same degree as HF→HFB (p < 0.05). Despite remaining on a HF obesogenic diet, introducing beans in established obesity improved the obese phenotype (intestinal health and adipose inflammation) more substantially than weight loss alone.