Mucosal immunoglobulins

Immune system and cholangiocytes: A puzzling affair in primary biliary cholangitis

Primary biliary cholangitis (PBC) is a cholestatic liver disease characterized by the destruction of the small and medium bile ducts. Its pathogenesis is still unknown. Despite the genome wide association study findings, the therapies targeting the cytokines pathway, tested so far, have failed. The concept of the biliary epithelium as a key player of the PBC pathogenesis has emerged over the last few years. It is now well accepted that the biliary epithelial cells (BECs) actively participate to the genesis of the damage. The chronic stimulation of BECs via microbes and bile changes the cell phenotype toward an active state, which, across the production of proinflammatory mediators, can recruit, retain, and activate immune cells. The consequent immune system activation can in turn damage BECs. Thus, the crosstalk between both innate and adaptive immune cells and the biliary epithelium creates a paracrine loop responsible for the disease progression. In this review, we summarize the evidence provided in literature about the role of BECs and the immune system in the pathogenesis of PBC. We also dissect the relationship between the immune system and the BECs, focusing on the unanswered questions and the future potential directions of the translational research and the cellular therapy in this area.

Structural insights into secretory immunoglobulin A and its interaction with a pneumococcal adhesin

Secretory Immunoglobulin A (SIgA) is the most abundant antibody at the mucosal surface. It possesses two additional subunits besides IgA: the joining chain (J-chain) and secretory component (SC). SC is the ectodomain of the polymeric immunoglobulin receptor (pIgR), which functions to transport IgA to the mucosa. How the J-chain and pIgR/SC facilitate the assembly and secretion of SIgA remains incompletely understood. Furthermore, during the infection of Streptococcus pneumoniae, the pneumococcal adhesin SpsA hijacks pIgR/SC and SIgA to gain entry to human cells and evade host defense. How SpsA targets pIgR/SC and SIgA also remains elusive. Here we report a cryo-electron microscopy structure of the Fc region of IgA1 (Fcα) in complex with the J-chain and SC (Fcα-J-SC), which reveals the organization principle of SIgA. We also present a structure of Fcα-J-SC complexed with SpsA, which uncovers the specific interactions between SpsA and human pIgR/SC. These results advance the molecular understanding of SIgA and shed light on S. pneumoniae pathogenesis.

Impact of IgA isoforms on their ability to activate dendritic cells and to prime T cells

Human IgA could be from different isotypes (IgA1/IgA2) and/or isoforms (monomeric, dimeric, or secretory). Monomeric IgA mainly IgA1 are considered as an anti-inflammatory isotype whereas dimeric/secretory IgA have clearly dual pro- and anti-inflammatory effects. Here, we show that IgA isotypes and isoforms display different binding abilities to FcαRI, Dectin-1, DC-SIGN, and CD71 on monocyte-derived dendritic cells (moDC). We describe that IgA regulate the expression of their own receptors and trigger modulation of moDC maturation. We also demonstrate that dimeric IgA2 and IgA1 induce different inflammatory responses leading to cytotoxic CD8⁺ T cells activation. moDC stimulation by dimeric IgA2 was followed by a strong pro-inflammatory effect. Our study highlights differences regarding IgA isotypes and isoforms in the context of DC conditioning. Further investigations are needed on the activation of adaptive immunity by IgA in the context of microbiota/IgA complexes during antibody-mediated immune selection.

Efficient N-Glycosylation of the Heavy Chain Tailpiece Promotes the Formation of Plant-Produced Dimeric IgA

Production of monomeric IgA in mammalian cells and plant expression systems such as Nicotiana benthamiana is well-established and can be achieved by co-expression of the corresponding light and heavy chains. In contrast, the assembly of dimeric IgA requires the additional expression of the joining chain and remains challenging especially in plant-based systems. Here, we examined factors affecting the assembly and expression of HER2 binding dimeric IgA1 and IgA2m(2) variants transiently produced in N. benthamiana. While co-expression of the joining chain resulted in efficient formation of dimeric IgAs in HEK293F cells, a mixture of monomeric, dimeric and tetrameric variants was detected in plants. Mass-spectrometric analysis of site-specific glycosylation revealed that the N-glycan profile differed between monomeric and dimeric IgAs in the plant expression system. Co-expression of a single-subunit oligosaccharyltransferase from the protozoan Leishmania major in N. benthamiana increased the N-glycosylation occupancy at the C-terminal heavy chain tailpiece and changed the ratio of monomeric to dimeric IgAs. Our data demonstrate that N-glycosylation engineering is a suitable strategy to promote the formation of dimeric IgA variants in plants.

Nasal mucus proteome and its involvement in allergic rhinitis

Introduction: Nasal mucus is the first line defense barrier against various pathogens including allergens. Proteins in nasal mucus maybe used as biomarkers for diagnosis or future therapeutic strategies. Proteomics opens the possibility to investigate whole human proteomes.

Areas Covered: We aimed to analyze the existing literature on nasal mucus and nasal secretions proteomic approaches especially in allergic rhinitis. A PubMed/Medline search was conducted entering the following keywords and combinations: “nasal mucus”, “nasal lavage fluid,” nasal secretions,” “nasal swabs,” “allergic rhinitis,” ”proteins,” and “proteomics.”

Expert opinion: The majority of studies focus on single proteins or protein groups mainly using ELISA techniques. Four studies met the criteria using mass spectrometry in the analysis of nasal mucus proteomes in rhinologic diseases. In these studies, 7, 35, 267, and 430 proteins were identified, respectively. These four studies are discussed in this review and put in relation to seven other proteomic studies that focus on nasal lavage fluid and nasal secretions obtained by swabs or filter paper. To put it in a nutshell, proteomics facilitates the investigation of the nasal secretome and its role in healthy and diseased state and as potential biomarkers for new diagnostic or therapeutic approaches.

Ganoderma atrum polysaccharide ameliorates intestinal mucosal dysfunction associated with autophagy in immunosuppressed mice

The aim of this study was to investigate the protective effect and underlying mechanisms of Ganoderma atrum polysaccharide (PSG-1) on cyclophosphamide (Cy)-induced intestinal mucosal dysfunction in mice. Results showed that PSG-1 promoted the formation of IgA-secreting cells, modulated sIgA, IgE, IgG, IgM secretion, and improved TLR-2, TLR-4, TLR-6 mRNA levels while these factors were suppressed after Cy treatment. CD4⁺ and CD8⁺ T cell numbers were also elevated by PSG-1. Cytokines including IFN-γ, TNF-α, IL-2, IL-12p70, IL-4, IL-1β, IL-17, IL-21, IL-23, TGF-β3 and transcription factors including T-bet, GATA-3, RORγt, Foxp3 increased after PSG-1 administration. Besides, PSG-1 reversed goblet cell numbers, and upregulated tight junction proteins like ZO-1, occludin and claudin-1 in immunosuppressed mice. Apart from these, the autophagy-related proteins LC3, Beclin-1, Atg5 and Atg7 were enhanced by PSG-1. These findings demonstrated that PSG-1 could ameliorate Cy-induced impairment of intestinal immunity and mucosal integrity, which maybe associated with autophagy in mice.

Food antigens and Transglutaminase 2 in IgA nephropathy: Molecular links between gut and kidney

The transglutaminase 2 (TG2) is one of the enigmatic enzymes with important functional diversity. It plays an important role in several pathologies such as celiac disease (CD). In patients with active CD, the abnormal retrotranscytosis of IgA/gliadin complexes is mediated by Transferrin Receptor 1 (TfR1). This triad association takes also place in IgA nephropathy (IgA-N). IgA-N is characterized by the formation of nephrotoxic complexes of IgA1 and soluble CD89 (sCD89). These complexes are abnormally deposited in the kidney. Using a humanized mouse model of IgA-N (α1KI-CD89Tg), we showed that IgA1-sCD89 complexes engender mesangial cell activation and proliferation with TfR1 and TG2 up-regulation, associated with IgA-N features. This TG2-TfR1 interaction enhances mesangial IgA1 deposition promoting inflammation. Humanized α1KI-CD89Tg mice deficient for TG2 show a decrease in TfR1 expression in kidney leading to reduced IgA1-sCD89 deposits and an improvement in IgA-N features. Moreover, TG2 is active and overexpressed in the intestine of IgA-N mice and gliadin participates to this renal pathology. In kidney as in intestine, the TG2 has a crucial role in the cooperation between TfR1-IgA and a central role in the pathogenic amplification.

Structural insights into immunoglobulin M

Immunoglobulin M (IgM) plays a pivotal role in both humoral and mucosal immunity. Its assembly and transport depend on the joining chain (J-chain) and the polymeric immunoglobulin receptor (pIgR), but the underlying molecular mechanisms of these processes are unclear. We report a cryo-electron microscopy structure of the Fc region of human IgM in complex with the J-chain and pIgR ectodomain. The IgM-Fc pentamer is formed asymmetrically, resembling a hexagon with a missing triangle. The tailpieces of IgM-Fc pack into an amyloid-like structure to stabilize the pentamer. The J-chain caps the tailpiece assembly and bridges the interaction between IgM-Fc and the polymeric immunoglobulin receptor, which undergoes a large conformational change to engage the IgM-J complex. These results provide a structural basis for the function of IgM.

Igh locus structure and evolution in Platyrrhines: new insights from a genomic perspective

Non-human primates have been used as animal models because of their phylogenetic closeness to humans. However, the genetic differences between humans and non-human primates must be considered to select the appropriate animal models. Recently, New World monkeys (Platyrrhines) have generated a higher interest in biomedical research, especially in assessing vaccine safety and immunogenicity. Given the continued and renewed interest in Platyrrhines as biomedical models, it is a necessary to have a better and more complete understanding of their immune system and its implications for research. Immunoglobulins (Ig) are the main proteins that mediate humoral immunity. These proteins have evolved as part of an adaptive immune response system derived from ancient vertebrates. There are at least four Ig classes in Prosimians, whereas five have been reported in Catarrhines. Information on the structure and evolution of the loci containing immunoglobulin heavy chain constant genes (Igh) in Platyrrhines, however, is limited. Here, Igh loci were characterized in 10 Platyrrhines using the available whole genome sequences. Human and Macaca Igh loci were also assessed to compare them with their Platyrrhines counterparts. Differences in Igh locus structure were observed between Platyrrhines and Catarrhines. Noteworthy changes occur in the γ gene, which encodes a key Ig involved in organism defense that would favor protection after vaccination. The remarkable differences between the immunoglobulin proteins of Platyrrhines and Catarrhines warrant a cautionary message to biomedical researchers.

The role of complement in IgA nephropathy

IgA nephropathy (IgAN) is common and often progresses to end stage renal disease. IgAN encompasses a wide range of histology and clinical features. IgAN pathogenesis is incompletely understood; the current multi-hit hypothesis of IgAN pathogenesis does not explain the range of glomerular inflammation and renal injury associated with mesangial IgA deposition. Although associations between IgAN and glomerular and circulating markers of complement activation are established, the mechanism of complement activation and contribution to glomerular inflammation and injury are not defined. Recent identification of specific complement pathways and proteins in severe IgAN cases had advanced our understanding of complement in IgAN pathogenesis. In particular, a growing body of evidence implicates the complement factor H related proteins 1 and 5 and lectin pathway as pathogenic in a subset of patients with severe disease. These data suggest complement deregulation and activity may be dominant drivers of renal injury in IgAN. Thereby, markers of complement activation may identify IgAN patients likely to progress to significant renal impairment and complement inhibition may emerge as an effective method of preventing and reducing glomerular injury in IgAN.

How to assess the effectiveness of nasal influenza vaccines? Role and measurement of sIgA in mucosal secretions

Secretory IgAs (sIgA) constitute the principal isotype of antibodies present in nasal and mucosal secretions. They are secreted by plasma cells adjacent to the mucosal epithelial cells, the site where infection occurs, and are the main humoral mediator of mucosal immunity. Mucosally delivered vaccines, such as live attenuated influenza vaccine (LAIV), are able to mimic natural infection without causing disease or virus transmission and mainly elicit a local immune response. The measurement of sIgA concentrations in nasal swab/wash and saliva samples is therefore a valuable tool for evaluating their role in the effectiveness of such vaccines. Here, we describe two standardized assays (enzyme‐linked immunosorbent assay and microneutralization) available for the quantification of sIgA and discuss the advantages and limitations of their use.

Glycosylation in health and disease

The glycome describes the complete repertoire of glycoconjugates composed of carbohydrate chains, or glycans, that are covalently linked to lipid or protein molecules. Glycoconjugates are formed through a process called glycosylation and can differ in their glycan sequences, the connections between them and their length. Glycoconjugate synthesis is a dynamic process that depends on the local milieu of enzymes, sugar precursors and organelle structures as well as the cell types involved and cellular signals. Studies of rare genetic disorders that affect glycosylation first highlighted the biological importance of the glycome, and technological advances have improved our understanding of its heterogeneity and complexity. Researchers can now routinely assess how the secreted and cell-surface glycomes reflect overall cellular status in health and disease. In fact, changes in glycosylation can modulate inflammatory responses, enable viral immune escape, promote cancer cell metastasis or regulate apoptosis; the composition of the glycome also affects kidney function in health and disease. New insights into the structure and function of the glycome can now be applied to therapy development and could improve our ability to fine-tune immunological responses and inflammation, optimize the performance of therapeutic antibodies and boost immune responses to cancer. These examples illustrate the potential of the emerging field of 'glycomedicine'.

Molecular cloning, expression analyses of polymeric immunoglobulin receptor gene and its variants in grass carp (Ctenopharyngodon idellus) and binding assay of the recombinant immunoglobulin-like domains

The Polymeric Immunoglobulin Receptor (pIgR) gene has been proved to play an important role in transporting polymeric immunoglobulin (Ig) in the mucosal tissues of mammals. pIgR gene also exists in teleost, but the genetic diversity and functions of this gene still need to be further explored. We obtained seven grass carp pIgR splicing transcripts, a full-length pIgR (CipIgR-1) and six truncated variants (CipIgR-2 to CipIgR-7). The full-length pIgR contained two immunoglobulin-like domains (ILD), a transmembrane domain (TMD) and a cytoplasmic domain (CyD). The CipIgR-2 lacked a small part in CyD, and CipIgR-3 lost TMD and CyD. Partial cDNA sequences of the other four grass carp pIgR variants (CipIgR-4 to CipIgR-7) were also cloned. The total expression levels of CipIgR and its variants in different tissues were detected by real-time quantitative PCR. The highest expression was found in the intestine, followed by the spleen and the skin. The function of the two extracellular ILDs of CipIgR was investigated based on its combining capacity with grass carp immunoglobulin M (IgM) and aquatic pathogenic bacteria. The cDNA sequences of two ILDs were cloned and expressed in Escherichia coli BL21 (DE3). Recombinant ILDs protein was purified and incubated with different bacteria respectively. Results of Western blot showed the recombinant protein could combine Bacillus subtilis, Vibrio parahaemolyticus, and Escherichia coli. In addition, binding activity of rILDs with grass carp IgM was detected. Collectively, these results indicated that multiple variants of pIgR gene in grass carp might be involved in the antibacterial immunity.

Intestinal Epithelial Cells-Derived Hypoxia-Inducible Factor-1α Is Essential for the Homeostasis of Intestinal Intraepithelial Lymphocytes

Hif-1α is a master regulator which involved in the transcriptional regulation of anti-inflammatory or cellular responding to hypoxia. Previous work shows that the absence of Hif-1α results in the destruction of intestinal epithelial cell (IEC) and abnormalities of intestinal barrier function. However, we know very little about other functions of Hif-1α on intestinal intraepithelial lymphocyte (IEL). Therefore, we generated a transgenic mouse (Hif1-α^ΔIEC mice), which was knocked out Hif1-α specifically in IECs, to study the effect of Hif1-α on IEL. IELs were isolated from the small intestine and colon of mice, respectively, and examined by flow cytometry and quantitative real-time PCR. All the cytokines expression was detected by quantitative real-time PCR. The NSAID enteropathy was induced by gavaged with 5 mg/kg indomethacin and the experimental colitis was induced by administration of 2.5% DSS. We found that the number of IELs is increased in Hif1-α ^ΔIEC mice. It is showed that knockout of Hif1-α in IECs led to significant changes in IEL phenotype, including a marked decline in the CD8αα⁺ and TCRγδ⁺ population. The reduction of CD8αα⁺ IELs is accompanied by increased apoptosis, decreased proliferation and weakened migration in Hif1-α^ΔIEC mice. Moreover, absence of intestinal epithelial Hif1-α markedly changed the population of IELs in NSAID-induced small intestinal injury and increased susceptibility to dextran sulfate sodium-induced colitis. In summary, our results first time demonstrate that IEC-derived Hif1-α is essential for maintaining IELs homeostasis and intestinal microbiota.

Molecular cloning of polymeric immunoglobulin receptor-like (pIgRL) in flounder (Paralichthys olivaceus) and its expression in response to immunization with inactivated Vibrio anguillarum

In the present work, the polymeric immunoglobulin receptor-like (pIgRL) from flounder (Paralichthys olivaceus) was firstly cloned and identified. The full length cDNA of flounder pIgRL was of 1393 bp including an open reading frame of 1053 bp, and the deduced pIgRL sequence encoded 350 amino acids, with a predicted molecular mass of 39 kDa. There were two immunoglobulin-like domains in flounder pIgRL. In healthy flounder, the transcriptional level of pIgRL was detected in different tissues by real-time PCR, showing the highest level in the skin and gills, and higher levels in the spleen and hindgut. After flounders were vaccinated with inactivated Vibrio anguillarum via intraperitoneal injection and immersion, the pIgRL mRNA level increased firstly and then declined in all tested tissues during 48 h, and the maximum expression levels in the gills, skin, spleen and hindgut in immersion group, or in the spleen, head kidney, skin and gills in injection group, were higher than in other tested tissues. In addition, recombinant protein of the extracellular region of flounder pIgRL was expressed in Escherichia coli BL21 (DE3), and rabbit anti-pIgRL polyclonal antibodies were prepared, which specifically reacted with the recombinant pIgRL, and a 39 kDa protein confirmed as natural pIgRL by liquid chromatography-mass spectrometry in skin mucus of flounder. Co-immunoprecipitation assay and western-blotting demonstrated that the pIgRL, together with IgM, could be immunoprecipitated by anti-pIgRL antibody in gut, skin and gill mucus of flounder, suggesting the existence of pIgRL-IgM complexes. These results indicated that the flounder pIgRL was probably involved in the mucosal IgM transportation and played important roles in mucosal immunity.

Effect of enteral glutamine supplementation for low-birth-weight infants on weight gain patterns and levels of fecal secretory immunoglobulin A

Aim

Glutamine is needed for optimal cell growth and for the immune system, especially in the enterocytes of gut mucosal immune responses. Low birth weight makes infants susceptible to glutamine depletion because nutrition is limited in the first week of life. To determine the effect of enteral glutamine supplementation on weight gain patterns and fecal secretory immunoglobulin A.

Material and Methods

This study is a double-blind, randomized controlled trial. Infants were randomly assigned to the glutamine group and placebo group. The glutamine group was supplemented with glutamine 400 mg/kg/day for 14 days, and placebo group received glucose 400 mg/kg/day for 14 days. The infants were observed for 30 days. Return-to-birth-weight, weight gain velocity, and fecal secretory immunoglobulin A levels were monitored during the study.

Results

Thirty-seven low-birth-weight infants were randomly assigned to the glutamine and placebo groups. The glutamine group had a shorter return-to-birth-weight time than the placebo group (8.1±0.9 vs. 11.0±1.6 days) and faster weight gain velocity (20.0±1.8 vs. 15.5±2.2 g/kg/day) (p<0.001). Secretory immunoglobulin A levels after glutamine supplementation were higher than in the placebo group (0.456±0.057 vs. 0.376±0.035 mg/g) (p<0.001). Levels of secretory immunoglobulin A after treatment in each group were increased. However, there was a significant difference before and after supplementation between the glutamine and placebo groups (0.247±0.024 vs. 0.140±0.016 mg/g) (p<0.001).

Conclusion

Enteral glutamine supplementation in low-birth-weight infants accelerates return to birth weight, increases the weight gain velocity, and the levels of fecal secretory immunoglobulin A.

Serum IgA1 shows increased levels of α2,6-linked sialic acid in breast cancer

The lectin Helix pomatia agglutinin (HPA) recognizes altered glycosylation in solid cancers and the identification of HPA binding partners in tumour tissue and serum is an important aim. Among the many HPA binding proteins, IgA1 has been reported to be the most abundant in liver metastases. In this study, the glycosylation of IgA1 was evaluated using serum samples from patients with breast cancer (BCa) and the utility of IgA1 glycosylation as a biomarker was assessed. Detailed mass spectrometric structural analysis showed an increase in disialo-biantennary N-linked glycans on IgA1 from BCa patients (p < 0.0001: non-core fucosylated; p = 0.0345: core fucosylated) and increased asialo-Thomsen-Friedenreich antigen (TF) and disialo-TF antigens in the O-linked glycan preparations from IgA1 of cancer patients compared with healthy control individuals. An increase in Sambucus nigra binding was observed, suggestive of increased α2,6-linked sialic acid on IgA1 in BCa. Logistic regression analysis showed HPA binding to IgA1 and tumour size to be significant independent predictors of distant metastases (χ ² 13.359; n = 114; p = 0.020) with positive and negative predictive values of 65.7% and 64.6%, respectively. Immunohistochemical analysis of tumour tissue samples showed IgA1 to be detectable in BCa tissue. This report provides a detailed analysis of serum IgA1 glycosylation in BCa and illustrates the potential utility of IgA1 glycosylation as a biomarker for BCa prognostication.

Defensive Driving: Directing HIV-1 Vaccine-Induced Humoral Immunity to the Mucosa with Chemokine Adjuvants

A myriad of pathogens gain access to the host via the mucosal route; thus, vaccinations that protect against mucosal pathogens are critical. Pathogens such as HIV, HSV, and influenza enter the host at mucosal sites such as the intestinal, urogenital, and respiratory tracts. All currently licensed vaccines mediate protection by inducing the production of antibodies which can limit pathogen replication at the site of infection. Unfortunately, parenteral vaccination rarely induces the production of an antigen-specific antibody at mucosal surfaces and thus relies on transudation of systemically generated antibody to mucosal surfaces to mediate protection. Mucosa-associated lymphoid tissues (MALTs) consist of a complex network of immune organs and tissues that orchestrate the interaction between the host, commensal microbes, and pathogens at these surfaces. This complexity necessitates strict control of the entry and exit of lymphocytes in the MALT. This control is mediated by chemoattractant chemokines or cytokines which recruit immune cells expressing the cognate receptors and adhesion molecules. Exploiting mucosal chemokine trafficking pathways to mobilize specific subsets of lymphocytes to mucosal tissues in the context of vaccination has improved immunogenicity and efficacy in preclinical models. This review describes the novel use of MALT chemokines as vaccine adjuvants. Specific attention will be placed upon the use of such adjuvants to enhance HIV-specific mucosal humoral immunity in the context of prophylactic vaccination.

Spec-seq unveils transcriptional subpopulations of antibody-secreting cells following influenza vaccination

Vaccines are among the most effective public health tools for combating certain infectious diseases such as influenza. The role of the humoral immune system in vaccine-induced protection is widely appreciated; however, our understanding of how antibody specificities relate to B cell function remains limited due to the complexity of polyclonal antibody responses. To address this, we developed the Spec-seq framework, which allows for simultaneous monoclonal antibody (mAb) characterization and transcriptional profiling from the same single cell. Here, we present the first application of the Spec-seq framework, which we applied to human plasmablasts after influenza vaccination in order to characterize transcriptional differences governed by B cell receptor (BCR) isotype and vaccine reactivity. Our analysis did not find evidence of long-term transcriptional specialization between plasmablasts of different isotypes. However, we did find enhanced transcriptional similarity between clonally related B cells, as well as distinct transcriptional signatures ascribed by BCR vaccine recognition. These data suggest IgG and IgA vaccine-positive plasmablasts are largely similar, whereas IgA vaccine-negative cells appear to be transcriptionally distinct from conventional, terminally differentiated, antigen-induced peripheral blood plasmablasts.

Secondary IgA nephropathy

IgA nephropathy is the most common primary glomerulonephritis worldwide. Its frequent coexistence with inflammatory, infectious, or malignant processes raises the possibility of a pathologic rather than coincidental association. Major strides have been made to elucidate the underlying pathophysiologic events that culminate in the development of primary IgA nephropathy. Whether secondary forms of the disease share common pathways triggered by underlying disorders or different mechanisms leading to similar pathologic findings remains to be determined. In this article we describe the most frequent etiologies for secondary IgA nephropathy and review the available literature for the pathophysiology.

M cell-dependent antigen uptake on follicle-associated epithelium for mucosal immune surveillance

The follicle-associated epithelium (FAE) covering mucosa-associated lymphoid tissue is distinct from the villous epithelium in cellular composition and functions. Interleukin-22 binding protein (IL-22BP), provided by dendritic cells at the sub-epithelial dome region, inhibits the IL-22-mediated secretion of antimicrobial peptides by the FAE. The Notch signal from stromal cells underneath the FAE diminishes goblet cell differentiation. These events dampen the mucosal barrier functions to allow luminal microorganisms to readily gain access to the luminal surface of the FAE. Furthermore, receptor activator of nucleic factor-kappa B ligand (RANKL) from a certain stromal cell type induces differentiation into microfold (M) cells that specialize in antigen uptake in the mucosa. Microfold (M) cells play a key role in mucosal immune surveillance by actively transporting external antigens from the gut lumen to the lymphoid follicle. The molecular basis of antigen uptake by M cells has been gradually identified in the last decade. For example, GPI-anchored molecules (e.g., glycoprotein 2 (GP2) and cellular prion protein (PrP^C)) and β1-integrin facilitate the transport of specific types of xenobiotics. The antigen transport by M cells initiates antigen-specific mucosal immune responses represented by the induction of secretory immunoglobulin A (S-IgA). Meanwhile, several invasive pathogens exploit M cells as a portal to establish a systemic infection. Recent findings have uncovered the molecular machinery of differentiation and functions of M cells.

Limited Innovations After More Than 65 Years of Immunoglobulin Replacement Therapy: Potential of IgA- and IgM-Enriched Formulations to Prevent Bacterial Respiratory Tract Infections

Patients with primary immunoglobulin deficiency have lower immunoglobulin levels or decreased immunoglobulin function, which makes these patients more susceptible to bacterial infection. Most prevalent are the selective IgA deficiencies (~1:3,000), followed by common variable immune deficiency (~1:25,000). Agammaglobulinemia is less common (~1:400,000) and is characterized by very low or no immunoglobulin production resulting in a more severe disease phenotype. Therapy for patients with agammaglobulinemia mainly relies on prophylactic antibiotics and the use of IgG replacement therapy, which successfully reduces the frequency of invasive bacterial infections. Currently used immunoglobulin preparations contain only IgG. As a result, concurrent IgA and IgM deficiency persist in a large proportion of agammaglobulinemia patients. Especially patients with IgM deficiency remain at risk for recurrent infections at mucosal surfaces, which includes the respiratory tract. IgA and IgM have multiple functions in the protection against bacterial infections at the mucosal surface. Because of their multimeric structure, both IgA and IgM are able to agglutinate bacteria efficiently. Agglutination allows for entrapment of bacteria in mucus that increases clearance from the respiratory tract. IgA is also important for blocking bacterial adhesion by interfering with bacterial adhesion receptors. IgM in its place is very well capable of activating complement, therefore, it is thought to be important in complement-mediated protection at the mucosal surface. The purpose of this Mini Review is to highlight the latest advances regarding IgA- and IgM-enriched immunoglobulin replacement therapy. We describe the different IgA- and IgM-enriched IgG formulations, their possible modes of action and potential to protect against respiratory tract infections in patients with primary immunoglobulin deficiencies.

Peculiarities of the formation and subsequent removal of the circulating immune complexes from the bloodstream during the process of digestion

Background: Large protein aggregates, known as circulating immune complexes (CICs), are formed in biological fluids as a result of the development of the body's immune response to various provoking factors. The kinetic characteristics of the formation and removal of immune complexes (ICs), their physical parameters, the isotypic composition of immunoglobulins (Igs) and the antigenic component of the CICs may reflect certain aspects of certain pathological and metabolic processes taking place in humans and animals. The aim of this study is to assess the kinetic characteristics of the formation and removal of the CICs that form in blood after eating. We also analyze the changes in the isotypic composition of Igs of ICs that accompany this biological process in rodents and humans. Methods: We identified the CICs, which differed in size and class of Igs, using dynamic light scattering. To remove ICs from the plasma, we used immune-affinity sedimentation. Monoclonal antibodies for the Igs of different isotypes were added to the plasma samples to determine the isotypic composition of the ICs. Results: A large number of ICs were formed in the blood of rats and humans after eating (food CICs). In rats, food ICs are almost immediately filtered in the liver, without circulating in the bloodstream through the body. In humans, the level of food ICs in the blood increases for 3.5 h after ingestion, then within 7-8 h their gradual removal takes place. It was found that in the process of digestion in humans, the isotypic composition of Igs in the CICs changes and becomes more diverse. Conclusions: The molecular-cellular mechanisms of the formation and utilization of food CICs in humans and rodents do not match completely.

Oral immunization with a Lactobacillus casei-based anti-porcine epidemic diarrhoea virus (PEDV) vaccine expressing microfold cell-targeting peptide Co1 fused with the COE antigen of PEDV

AIMS

The aims of this study were to develop an effective M cell-targeting oral vaccine, involving Lactobacillus casei to deliver the porcine epidemic diarrhoea virus (PEDV) core neutralizing epitope (COE) antigen conjugated with M cell-targeting peptide Co1 as an adjuvant, against PEDV infection.

METHODS AND RESULTS

Genetically engineered L. casei 393 (L393) strains expressing PEDV COE antigen only (pPG-COE/L393) or fused-expressing COE and M cell-targeting peptide Co1 (pPG-COE-Co1/L393) were constructed, and the immunogenicity upon administration as an oral vaccine was evaluated. The results showed that higher anti-PEDV serum IgG and mucosal SIgA antibody responses were induced in mice orally immunized with strain pPG-COE-Co1/L393 as compared to the mice immunized with strain L393 expressing COE alone or carrying the empty plasmid. In addition, the use of the Co1 ligand elicited a splenocyte proliferative response more effectively in comparison with the COE antigen alone and supported a skewed T helper 2 type of immune response against PEDV.

CONCLUSIONS

pPG-COE-Co1/L393 can effectively induce mucosal, humoural and Th2-type cellular immune responses against PEDV infection via oral administration. Furthermore, M cell-targeting peptide ligand Co1 is a good mucosal adjuvant.

SIGNIFICANCE AND IMPACT OF THE STUDY

Lactobacillus casei delivering the COE antigen of PEDV conjugated with a M cell-targeting peptide Co1 as an immune adjuvant is a promising oral vaccine candidate for PEDV.

Effects of Isatis root polysaccharide in mice infected with H3N2 swine influenza virus

Isatis root polysaccharide (IRPS) has gained attention in the field of virology. However, very few studies have evaluated the effects of IRPS on H3N2 swine influenza virus (SIV). The antiviral activities of IRPS against SIV were investigated in vitro through three different modes and in vivo in an experimental mouse model of SIV infection. Mice were treated by oral gavage with various doses of IRPS before being experimentally infected with SIV A/swine/Henan/2010(H3N2). The antiviral effects of IRPS were evaluated by clinical signs, weight, histopathology, cytokine levels in lung homogenates and serum nitric oxide (NO) and IgG levels at 2, 5 and 9 d post-infection. IRPS demonstrated an inhibitory effect on SIV in Madin-Darby canine kidney cells. Additionally, IRPS significantly improved symptoms, reduced pathological changes and enhanced serum levels of NO and IgG in SIV-infected mice. Furthermore, detection of cytokines in lung homogenates showed IRPS could alter cytokine production to improve immune responses and systemic ability to repair inflammation. Moreover, IRPS extenuated the pulmonary inflammatory response. The results show that various concentrations of IRPS exert antiviral effects in vitro and in vivo. In an experimental mouse model of SIV infection, IRPS at a dose of 75 mg/kg was effective.

Characterization of HIV-1 gp120 antibody specificities induced in anogenital secretions of RV144 vaccine recipients after late boost immunizations

Sexual transmission is the principal driver of the human immunodeficiency virus (HIV) pandemic. Understanding HIV vaccine-induced immune responses at mucosal surfaces can generate hypotheses regarding mechanisms of protection, and may influence vaccine development. The RV144 (ClinicalTrials.gov NCT00223080) efficacy trial showed protection against HIV infections but mucosal samples were not collected, therefore, the contribution of mucosal antibodies to preventing HIV-1 acquisition is unknown. Here, we report the generation, magnitude and persistence of antibody responses to recombinant gp120 envelope and antigens including variable one and two loop scaffold antigens (gp70V1V2) previously shown to correlate with risk in RV144. We evaluated antibody responses to gp120 A244gD and gp70V1V2 92TH023 (both CRF01_AE) and Case A2 (subtype B) in cervico-vaginal mucus (CVM), seminal plasma (SP) and rectal secretions (RS) from HIV-uninfected RV144 vaccine recipients, who were randomized to receive two late boosts of ALVAC-HIV/AIDSVAX®B/E, AIDSVAX®B/E, or ALVAC-HIV alone at 0 and 6 months. Late vaccine boosting increased IgG geometric mean titers (GMT) to gp120 A244gD in AIDSVAX®B/E and ALVAC-HIV/AIDSVAX®B/E CVM (28 and 17 fold, respectively), followed by SP and RS. IgG to gp70V1V2 92TH023 increased in AIDSVAX®B/E and ALVAC-HIV/AIDSVAX®B/E CVM (11–17 fold) and SP (2 fold) two weeks post first boost. IgG to Case A2 was only detected in AIDSVAX®B/E and ALVAC-HIV/AIDSVAX®B/E CVM. Mucosal IgG to gp120 A244gD (CVM, SP, RS), gp70V1V2 92TH023 (CVM, SP), and Case A2 (CVM) correlated with plasma IgG levels (p<0.001). Although the magnitude of IgG responses declined after boosting, anti-gp120 A244gD IgG responses in CVM persisted for 12 months post final vaccination. Further studies in localization, persistence and magnitude of envelope specific antibodies (IgG and dimeric IgA) in anogenital secretions will help determine their role in preventing mucosal HIV acquisition.

Circulating pathogen-specific plasmablasts in female patients with upper genital tract infection

Mucosal antibodies constitute the first line of adaptive immune defence against invaders in the female genital tract (FGT), yet the sequence of events leading to their production is surprisingly poorly characterized. We explored the induction of pathogen-specific antibody-secreting cells (ASC) as a response to an acute infection in the upper FGT. We recruited 12 patients undergoing surgery due to an upper FGT infection (7/12 blood culture positive, 5/12 negative) and six healthy controls. Pathogens were sampled during surgery and PBMC collected in the acute phase of the disease (days 7-10). We searched by ELISPOT circulating pathogen-specific ASC and explored their frequency, immunoglobulin isotype distribution, and expressions of homing receptors (α₄β_7, L-selectin, and CLA). All patients had circulating ASC specific to the infective bacteria; the geometric mean was 434 (95%CI 155-1234) ASC (IgA + IgG + IgM)/10⁶ PBMC. IgA ASC predominated in 7/12, IgG ASC in 3/12, and IgM ASC in 2/12 cases. Of all the pathogen-specific ASC, 60% expressed α₄β₇, 67% L-selectin, and 9% CLA. This study is the first to show induction of pathogen-specific ASC in the peripheral blood in bacterial infection in the human FGT. Our findings reveal that such FGT-originating pathogen-specific ASC are predominated by IgA ASC and exhibit a homing receptor profile resembling that of ASC in acute urinary tract infection. The data thus suggest a characteristic profile shared by the urogenital tract.

Short communication: Immune responses in sows induced by porcine sapovirus virus-like particles reduce viral shedding in suckled piglets

Porcine sapovirus (PoSaV) is a potential threat to public health owing to its capacity for reassortment with human sapovirus strains. However, there is still no vaccine available for the prevention and control of this infectious disease. In this study, we developed PoSaV virus-like particles (VLPs) using a baculovirus expression system. Immunization with PoSaV VLPs induced high titers of serum antibody specific for VP1 in sows. The results of our challenge study demonstrated that maternally-derived antibodies (MDA) induced by VLP immunization dramatically reduced viral shedding of PoSaV in the feces of next generation piglets. Therefore, the results of this study indicate that the immune responses of sows elicited by PoSaV VLPs can inhibit in vivo viral replication in their offspring and represent a promising strategy for developing vaccines against PoSaV.

Respiratory syncytial virus elicits enriched CD8+ T lymphocyte responses in lung compared with blood in African green monkeys

Respiratory syncytial virus (RSV) is a leading cause of serious lower respiratory tract disease in young children and older adults throughout the world. Prevention of severe RSV disease through active immunization is optimal but no RSV vaccine has been licensed so far. Immune mechanisms of protection against RSV infection in humans have not been fully established, thus a comprehensive characterization of virus-specific immune responses in a relevant animal model will be beneficial in defining correlates of protection. In this study, we infected juvenile naive AGMs with RSV A2 strain and longitudinally assessed virus-specific humoral and cellular immune responses in both peripheral blood and the respiratory tract. RSV viral loads at nasopharyngeal surfaces and in the lung peaked at around day 5 following infection, and then largely resolved by day 10. Low levels of neutralizing antibody titers were detected in serum, with similar kinetics as RSV fusion (F) protein-binding IgG antibodies. RSV infection induced CD8+, but very little CD4+, T lymphocyte responses in peripheral blood. Virus-specific CD8+ T cell frequencies were ~10 fold higher in bronchoaveolar lavage (BAL) compared to peripheral blood and exhibited effector memory (CD95+CD28-) / tissue resident memory (CD69+CD103+) T (TRM) cell phenotypes. The kinetics of virus-specific CD8+ T cells emerging in peripheral blood and BAL correlated with declining viral titers, suggesting that virus-specific cellular responses contribute to the clearance of RSV infection. RSV-experienced AGMs were protected from subsequent exposure to RSV infection. Additional studies are underway to understand protective correlates in these seropositive monkeys.

Effects of Cordyceps militaris spent mushroom substrate and Lactobacillus plantarum on mucosal, serum immunology and growth performance of Nile tilapia (Oreochromis niloticus)

An 8-weeks feeding trial was performed to investigate the possible effects of supplementation of Nile tilapia diet with Cordyceps militaris spent mushroom substrate (SMS) single or combined with Lactobacillus plantarum on immune parameters and growth performance. For this aim, Nile tilapia fingerlings were fed with four experimental diets namely: Diet 1 (0 - control), Diet 2 (10 g kg^-1 SMS), Diet 3 (10⁸ CFU g^-1L. plantarum), and Diet 4 (10 g kg^-1 SMS + 10⁸ CFU g^-1L. plantarum). At the end of feeding trial, skin mucus parameters, serum immune parameters, and growth performance were measured. The results indicated that supplementations SMS + L. plantarum or/and resulted in a significant increase in skin mucus lysozyme and peroxidase activities compared with the control group after 8 weeks of feeding trial (P < 0.05). The highest values of these parameters were recorded for fish fed both SMS + L. plantarum supplementations. Nonetheless, no significant difference was recorded between other supplemented groups (P < 0.05). For serum immunology, the results showed that serum lysozyme activity, alternative complement, phagocytosis, serum peroxidase, and respiratory burst activities were significantly higher in supplemented groups compared to the control (P < 0.05). The highest values were recorded in fish fed both SMS and L. plantarum with respect to the individual application. No significant differences were observed between fish fed SMS and L. plantarum (P < 0.05). Results on growth performance indicated that fish fed supplemented diets showed a statistically significant increase in the specific growth rate (SGR), weight gain (WG), final weight (FW) compared to the control group (P < 0.05). The highest SGR and WG values were observed in fish fed both dietary SMS and L. plantarum. However, no significant differences in these parameters were observed in fish fed SMS or L. plantarum alone (P > 0.05). The FCR was significantly lower in fish fed 10 g kg^-1 SMS + 10⁸ CFU g^-1L. plantarum than in other groups, while control group presented the highest values (P < 0.05). The present results suggested that the combination of these natural substances could be considered as potential feed-additives for aquaculture farmed fish.

Radiolabelled polymeric IgA: from biodistribution to a new molecular imaging tool in colorectal cancer lung metastases

By radiolabelling monomeric (m) and polymeric (p) IgA with technetium 99m (99mTc), this study assessed IgA biodistribution and tumour-targeting potency. IgA directed against carcinoembryonic antigen (CEA), a colorectal cancer marker, was selected to involve IgA mucosal tropism. Ig was radiolabelled with 99mTc-tricarbonyl after derivatisation by 2-iminothiolane. 99mTc-IgA was evaluated by in vitro analysis. The biodistributions of radiolabelled anti-CEA mIgA, pIgA and IgG were compared in normal mice. Anti-CEA pIgA tumour uptake was studied in mice bearing the WiDr caecal orthotopic graft. IgA radiolabelling was obtained with a high yield, was stable in PBS and murine plasma, and did not alter IgA binding functionality (Kd ≈ 25 nM). Biodistribution studies in normal mice confirmed that radiolabelled pIgA - and to a lesser extent, mIgA - showed strong and fast mucosal tropism and a shorter serum half-life than IgG. In caecal tumour model mice, evaluation of the anti-CEA-pIgA biodistribution showed a high uptake in lung metastases, confirmed by histological analysis. However, no radioactivity uptake increase in the tumoural caecum was discerned from normal intestinal tissue, probably due to high IgA caecal natural tropism. In microSPECT/CT imaging, 99mTc-IgA confirmed its diagnostic potency of tumour in mucosal tissue, even if detection threshold by in vivo imaging was higher than post mortem studies. Contribution of the FcαRI receptor, studied with transgenic mouse model (Tsg SCID-CD89), did not appear to be determinant in 99mTc-IgA uptake. Pre-clinical experiments highlighted significant differences between 99mTc-IgA and 99mTc-IgG biodistributions. Furthermore, tumoural model studies suggested potential targeting potency of pIgA in mucosal tissues.

Mucosal Administration of Cycle-Di-Nucleotide-Adjuvanted Virosomes Efficiently Induces Protection against Influenza H5N1 in Mice

The need for more effective influenza vaccines is highlighted by the emergence of novel influenza strains, which can lead to new pandemics. There is a growing population of susceptible subjects at risk for severe complications of influenza, such as the elderly who are only in part protected by current licensed seasonal vaccines. One strategy for improving seasonal and pandemic vaccines takes advantage of adjuvants to boost and modulate evoked immune responses. In this study, we examined the capacity of the recently described adjuvant cyclic di-adenosine monophosphate (c-di-AMP) to serve as an adjuvant for improved mucosal influenza vaccines, and induce effective protection against influenza H5N1. In detail, c-di-AMP promoted (i) effective local and systemic humoral immune responses, including protective hemagglutination inhibition titers, (ii) effective cellular responses, including multifunctional T cell activity, (iii) induction of long-lasting immunity, and (iv) protection against viral challenge. Furthermore, we demonstrated the dose-sparing capacity of the adjuvant as well as the ability to evoke cross-clade protective immune responses. Overall, our results suggest that c-di-AMP contributes to the generation of a protective cell-mediated immune response required for efficacious vaccination against influenza, which supports the further development of c-di-AMP as an adjuvant for seasonal and pandemic influenza mucosal vaccines.

Peptide mimetics of immunoglobulin A (IgA) and FcαRI block IgA-induced human neutrophil activation and migration

The cross‐linking of the IgA Fc receptor (FcαRI) by IgA induces release of the chemoattractant LTB4, thereby recruiting neutrophils in a positive feedback loop. IgA autoantibodies of patients with autoimmune blistering skin diseases therefore induce massive recruitment of neutrophils, resulting in severe tissue damage. To interfere with neutrophil mobilization and reduce disease morbidity, we developed a panel of specific peptides mimicking either IgA or FcαRI sequences. CLIPS technology was used to stabilize three‐dimensional structures and to increase peptides’ half‐life. IgA and FcαRI peptides reduced phagocytosis of IgA‐coated beads, as well as IgA‐induced ROS production and neutrophil migration in in vitro and ex vivo (human skin) experiments. Since topical application would be the preferential route of administration, Cetomacrogol cream containing an IgA CLIPS peptide was developed. In the presence of a skin permeation enhancer, peptides in this cream were shown to penetrate the skin, while not diffusing systemically. Finally, epitope mapping was used to discover sequences important for binding between IgA and FcαRI. In conclusion, a cream containing IgA or FcαRI peptide mimetics, which block IgA‐induced neutrophil activation and migration in the skin may have therapeutic potential for patients with IgA‐mediated blistering skin diseases.

Complex immune correlates of protection in HIV-1 vaccine efficacy trials

Development of an efficacious HIV-1 vaccine is a major priority for improving human health worldwide. Vaccine-mediated protection against human pathogens can be achieved through elicitation of protective innate, humoral, and cellular responses. Identification of specific immune responses responsible for pathogen protection enables vaccine development and provides insights into host defenses against pathogens and the immunological mechanisms that most effectively fight infection. Defining immunological correlates of transmission risk in preclinical and clinical HIV-1 vaccine trials has moved the HIV-1 vaccine development field forward and directed new candidate vaccine development. Immune correlate studies are providing novel hypotheses about immunological mechanisms that may be responsible for preventing HIV-1 acquisition. Recent results from HIV-1 immune correlates work has demonstrated that there are multiple types of immune responses that together, comprise an immune correlate-thus implicating polyfunctional immune control of HIV-1 transmission. An in depth understanding of these complex immunological mechanisms of protection against HIV-1 will accelerate the development of an efficacious HIV-1 vaccine.

Functional and structural characteristics of secretory IgA antibodies elicited by mucosal vaccines against influenza virus

Mucosal tissues are major targets for pathogens. The secretions covering mucosal surfaces contain several types of molecules that protect the host from infection. Among these, mucosal immunoglobulins, including secretory IgA (S-IgA) antibodies, are the major contributor to pathogen-specific immune responses. IgA is the primary antibody class found in many external secretions and has unique structural and functional features not observed in other antibody classes. Recently, extensive efforts have been made to develop novel vaccines that induce immunity via the mucosal route. S-IgA is a key molecule that underpins the mechanism of action of these mucosal vaccines. Thus, precise characterization of S-IgA induced by mucosal vaccines is important, if the latter are to be used successfully in a clinical setting. Intensive studies identified the fundamental characteristics of S-IgA, which was first discovered almost half a century ago. However, S-IgA itself has not gained much attention of late, despite its importance to mucosal immunity; therefore, some important questions remain. This review summarizes the current understanding of the molecular characteristics of S-IgA and its role in intranasal mucosal vaccines against influenza virus infection.

Bile Acid Administration Elicits an Intestinal Antimicrobial Program and Reduces the Bacterial Burden in Two Mouse Models of Enteric Infection

In addition to their chemical antimicrobial nature, bile acids are thought to have other functions in the homeostatic control of gastrointestinal immunity. However, those functions have remained largely undefined. In this work, we used ileal explants and mouse models of bile acid administration to investigate the role of bile acids in the regulation of the intestinal antimicrobial response. Mice fed on a diet supplemented with 0.1% chenodeoxycholic acid (CDCA) showed an upregulated expression of Paneth cell α-defensins as well as an increased synthesis of the type-C lectins Reg3b and Reg3g by the ileal epithelium. CDCA acted on several epithelial cell types, by a mechanism independent from farnesoid X receptor (FXR) and not involving STAT3 or β-catenin activation. CDCA feeding did not change the relative abundance of major commensal bacterial groups of the ileum, as shown by 16S analyses. However, administration of CDCA increased the expression of ileal Muc2 and induced a change in the composition of the mucosal immune cell repertoire, decreasing the proportion of Ly6G⁺ and CD68⁺ cells, while increasing the relative amount of IgGκ⁺ B cells. Oral administration of CDCA to mice attenuated infections with the bile-resistant pathogens Salmonella enterica serovar Typhimurium and Citrobacter rodentium, promoting lower systemic colonization and faster bacteria clearance, respectively. Our results demonstrate that bile acid signaling in the ileum triggers an antimicrobial program that can be potentially used as a therapeutic option against intestinal bacterial infections.

A role for whey-derived lactoferrin and immunoglobulins in the attenuation of obesity-related inflammation and disease

Obesity is a strong predictive factor in the development of chronic disease and has now superseded undernutrition as a major public health issue. Chronic inflammation is one mechanism thought to link excess body weight with disease. Increasingly, the gut and its extensive population of commensal microflora are recognized as playing an important role in the development of obesity-related chronic inflammation. Obesity and a high fat diet are associated with altered commensal microbial communities and increased intestinal permeability which contributes to systemic inflammation as a result of the translocation of lipopolysaccharide into the circulation and metabolic endotoxemia. Various milk proteins are showing promise in the prevention and treatment of obesity and chronic low-grade inflammation via reductions in visceral fat, neutralization of bacteria at the mucosa and reduced intestinal permeability. In this review, we focus on evidence supporting the potential antiobesogenic and anti-inflammatory effects of bovine whey-derived lactoferrin and immunoglobulins.

Randomized, double-blind, placebo-controlled, parallel-group study of the effect of Lactobacillus paracasei K71 intake on salivary release of secretory immunoglobulin A

Lactobacillus paracasei K71 was shown to be effective in alleviating the severity of atopic dermatitis in a randomized controlled trial, and a preliminary open-label trial suggested that strain K71 intake enhanced secretory immunoglobulin A (sIgA) release in the saliva. This study investigated the effect of K71 on sIgA release in a randomized, double-blind, placebo-controlled, parallel-group trial. The trial included 62 Japanese subjects aged 20–64 years with relatively low rates of salivary sIgA release. Subjects (n=31 in each group) were randomly given a tablet containing 100 mg (approximately 2 × 10¹¹ bacteria) of K71 or a placebo tablet daily for 12 weeks. After eliminating data for eight subjects (four in each group) who met the exclusion criteria for efficacy analysis, data for 54 subjects were analyzed. The change in the rate of salivary sIgA release 8 weeks after initiation of the study compared with baseline was significantly higher in the K71 tablet group (105.5 ± 119.0 µg/min) than in the placebo group (52.7 ± 62.6 µg/min; p=0.047). There were no adverse events associated with intake of tablets containing K71. The safety of intake of L. paracasei K71 was also confirmed in an independent open-label trial with 20 healthy subjects who consumed excessive amounts of K71-containing food. L. paracasei K71 intake may therefore have some benefits in promoting mucosal immune function.

Glyco-engineering for the production of recombinant IgA1 with distinct mucin-type O-glycans in plants

IgA nephropathy (IgAN) is a common autoimmune disease that is characterized by formation and deposition of IgA1-containing immune complexes frequently leading to end-stage kidney disease. The IgA1 in these immune complexes carries aberrantly glycosylated O-glycans. In circulating IgA1 these galactose-deficient mucin-type O-glycans are bound by autoantibodies and thus, contribute to immune complex formation and pathogenesis. Even though the disease is associated with the overproduction of aberrant O-glycans on IgA1, specific structure-function-studies of mucin-type O-glycans are limited. Compared to other expression hosts, plants offer the opportunity for de novo synthesis of O-glycans on recombinant glycoproteins as they are lacking the mammalian O-glycosylation pathway. Recently, we demonstrated that Nicotiana benthamiana are suitable for the generation of distinct O-glycans on recombinant IgA1. Here, we expand our engineering repertoire by in planta generation of galactose-deficient and α2,6-sialylated O-glycans which are the prevailing glycans detected on IgA1 from patients with IgAN.

Component-resolved analysis of IgA, IgE, and IgG4 during egg OIT identifies markers associated with sustained unresponsiveness

BACKGROUND

In a previously reported CoFAR study, 55 subjects with egg allergy underwent randomized, placebo-controlled egg oral immunotherapy (eOIT). Active treatment induced desensitization in most and sustained unresponsiveness (SU) in a smaller subset. We hypothesized that component-resolved analysis of IgE, IgG4, IgA, IgA1, and IgA2 may identify potential biomarkers of SU in OIT subjects.

METHODS

Longitudinal samples for 51 egg-allergic subjects (37 active and 14 placebo) were available. Egg white (EW)-, ovalbumin (OVA)-, and ovomucoid (OVM)-specific levels of IgA, IgA1, and IgA2 were quantified by ELISA. IgE and IgG4 to these antigens were quantified using ImmunoCAP^® . Clinical responders achieved SU to egg; all others were considered nonresponders. Between-group comparisons were made among active and placebo, as well as responders and nonresponders.

RESULTS

No placebo subjects achieved responder status. Through month 48, among the 37 active subjects, baseline IgE-OVM was lower in responders (median 3.97 kU/l, n = 19) than in nonresponders (10.9 kU/l, n = 18, P = 0.010). Logistic regression analysis revealed that lower baseline IgE-EW (P = 0.038), IgE-OVM (P = 0.032), and a higher IgG4/IgE-OVM ratio (P = 0.013) were associated with clinical response. Relative increases in IgG4-EW, IgA-EW, and IgA2-EW were observed in responders (P = 0.024, 0.024, and 0.029, respectively). IgG4/IgE, IgA/IgE, and IgA2/IgE ratios for EW and IgA/IgE ratio for OVA were found to be significantly elevated among responders (P = 0.004, 0.009, 0.028, and 0.008, respectively).

CONCLUSIONS

Increased IgG4-EW, IgA-EW, and IgA2-EW during eOIT are associated with clinical response to eOIT. Lower pretreatment IgE-EW and IgE-OVM are also associated with SU. Future studies are needed to evaluate and validate these potential biomarkers.

The long and winding road to IgA deficiency: causes and consequences

INTRODUCTION

The most common humoral immunodeficiency is IgA deficiency. One of the first papers addressing the cellular and molecular mechanisms underlying IgA deficiency indicated that immature IgA-positive B-lymphocytes are present in these patients. This suggests that the genetic background for IgA is still intact and that class switching can take place. At this moment, it cannot be ruled out that genetic as well as environmental factors are involved. Areas covered: A clinical presentation, the biological functions of IgA, and the management of IgA deficiency are reviewed. In some IgA deficient patients, a relationship with a loss-of-function mutation in the TACI (transmembrane activator and calcium-modulating cyclophilin ligand interaction) gene has been found. Many other genes also have been associated. Gut microbiota are an important environmental trigger for IgA synthesis. Expert commentary: Expression of IgA deficiency is due to both genetic and environmental factors and a role for gut microbiota cannot be excluded.

Immunoglobulin A nephropathy: a pathophysiology view

BACKGROUND AND AIM

IgA nephropathy is one of the leading causes of primary glomerulonephritis worldwide and an important etiology of renal disease in young adults. IgA nephropathy is considered an immune complex-mediated disease.

METHODS

This review article summarizes recent evidence on the pathophysiology of IgA nephropathy.

RESULTS

Current studies indicate an ordered sequence of multi-hits as fundamental to disease occurrence. Altered glycan structures in the hinge region of the heavy chains of IgA1 molecules act as auto-antigens, potentially triggering the production of glycan-specific autoantibodies. Recognition of novel epitopes by IgA and IgG antibodies leads to the formation of immune complexes galactose deficient-IgA1/anti-glycan IgG or IgA. Immune complexes of IgA combined with FcαRI/CD89 have also been implicated in disease exacerbation. These nephritogenic immune complexes are formed in the circulation and deposited in renal mesangium. Deposited immune complexes ultimately induce glomerular injury, through the release of pro-inflammatory cytokines, secretion of chemokines and the resultant migration of macrophages into the kidney. The TfR1/CD71 receptor has a pivotal role in mesangial cells. New signaling intracellular mechanisms have also been described.

CONCLUSION

The knowledge of the whole pathophysiology of this disease could provide the rational bases for developing novel approaches for diagnosis, for monitoring disease activity, and for disease-specific treatment.

Immunoglobulin Tau Heavy Chain (IgT) in Flounder, Paralichthys olivaceus: Molecular Cloning, Characterization, and Expression Analyses

Immunoglobulin tau (IgT) is a new teleost immunoglobulin isotype, and its potential function in adaptive immunity is not very clear. In the present study, the membrane-bound and secreted IgT (mIgT and sIgT) heavy chain genes were cloned for the first time and characterized in flounder (Paralichthys olivaceus), and found the nucleic acid sequence were exactly same in the Cτ1–Cτ4 constant domains of mIgT and sIgT, but different in variable regions and the C-terminus. The amino acid sequence of mIgT shared higher similarity with Bovichtus diacanthus (51.2%) and Dicentrarchus labrax (45.0%). Amino acid of flounder IgT, IgM, and IgD heavy chain was compared and the highest similarity was found between IgT Cτ1 and IgM Cμ1 (38%). In healthy flounder, the transcript levels of IgT mRNA were the highest in gill, spleen, and liver, and higher in peripheral blood leucocytes, skin, and hindgut. After infection and vaccination with Edwardsiella tarda via intraperitoneal injection and immersion, the qRT-PCR analysis demonstrated that the IgT mRNA level was significantly upregulated in all tested tissues, with similar dynamic tendency that increased firstly and then decreased, and higher in gill, skin, hindgut, liver, and stomach in immersion than in the injection group, but no significant difference existed in spleen and head kidney between immersion and injection groups. These results revealed that IgT responses could be simultaneously induced in both mucosal and systemic tissues after infection/vaccination via injection and immersion route, but IgT might play a more important role in mucosal immunity than in systemic immunity.

Immunogenicity of an S1D epitope from porcine epidemic diarrhea virus and cholera toxin B subunit fusion protein transiently expressed in infiltrated Nicotiana benthamiana leaves

Porcine epidemic diarrhea virus (PEDV) belongs to the Coronaviridae family and causes acute enteritis in pigs. A fragment of the large spike glycoprotein, termed the S1D epitope (aa 636-789), alone and fused with cholera toxin B subunit, were independently cloned into plant expression vectors, yielding plasmids pMYV717 and pMYV719, respectively. Plant expression vectors were transformed into Agrobacterium tumefaciens and subsequently infiltrated into Nicotiana benthamiana leaves. The highest expression level of S1D was found at 2 days post infiltration (dpi), reached 0.04 % of total soluble protein, and rapidly decreased thereafter. The expression and assembly of CTB-S1D fusion protein were confirmed by Western blot and GM1-ELISA. The highest expression level of CTB-S1D fusion protein was 0.07 % of TSP at 4 dpi, with a rapid decrease thereafter. In the presence of p19 protein from tomato bushy stunt virus, the S1D and CTB-S1D protein levels peaked at 6 dpi and were fourfold to sevenfold higher than in the absence of p19, respectively. After oral administration of transiently expressed CTB-S1D fusion protein, or with bacterial cholera toxin or rice callus expressing mutant cholera toxin 61F, mice exhibited significantly greater serum IgG and sIgA levels against bacterial CTB and S1D antigen, peaking at week 6. Transiently expressed CTB-S1D fusion protein will be administered orally to pigs to assess the immune response against PEDV.

Intake of black-vinegar-mash-garlic enhances salivary release of secretory IgA: A randomized, double-blind, placebo-controlled, parallel-group study

Several previous studies have provided evidence that suggests the beneficial effects of garlic and black vinegar on human health, including benefits to immune function. The preliminary study indicated that the intake of black-vinegar-mash-garlic-containing food, created from aged garlic pickled in the mash of black vinegar, enhanced the release of secretory immunoglobulin A (sIgA) in the saliva. The aim of the present study was to evaluate the effect of the food in a randomized, double-blind, placebo-controlled, parallel-group trial. The trial was conducted in subjects aged between 30 and 60 years whose rate of salivary sIgA release was moderately low. Subjects consumed 2.49 g of placebo or black-vinegar-mash-garlic-containing food (active food) daily for 8 weeks. The data obtained with 54 eligible subjects (n=28 and 26 for placebo and active, respectively) were analyzed for efficacy. The rates of salivary sIgA release in the active food group (35.9±84.6 and 47.9±123.4 µg/min at weeks 4 and 8 of intake; changes from pretrial value) were higher compared to the respective rates in the placebo food group (-12.3±72.1 and -3.2±85.9 µg/min, P=0.028 and 0.082, respectively). These findings indicate that intake of black-vinegar-mash-garlic-containing food enhanced the intraoral immune response. There was no adverse event associated with the intake of active food.

Distinct genital tract HIV-specific antibody profiles associated with tenofovir gel

The impact of topical antiretrovirals for pre-exposure prophylaxis on humoral responses following HIV infection is unknown. Using a binding antibody multiplex assay, we investigated HIV-specific IgG and IgA responses to envelope glycoproteins, p24 Gag and p66, in the genital tract (GT) and plasma following HIV acquisition in women assigned to tenofovir gel (n=24) and placebo gel (n=24) in the CAPRISA 004 microbicide trial to assess if this topical antiretroviral had an impact on mucosal and systemic antibody responses. Linear mixed effect modeling and partial least squares discriminant analysis was used to identify multivariate antibody signatures associated with tenofovir use. There were significantly higher response rates to gp120 Env (P=0.03), p24 (P=0.002), and p66 (P=0.009) in plasma and GT in women assigned to tenofovir than placebo gel at multiple time points post infection. Notably, p66 IgA titers in the GT and plasma were significantly higher in the tenofovir compared with the placebo arm (P<0.05). Plasma titers for 9 of the 10 HIV-IgG specificities predicted GT levels. Taken together, these data suggest that humoral immune responses are increased in blood and GT of individuals who acquire HIV infection in the presence of tenofovir gel.