Mouse IgA modulates human gut microbiota with inflammatory bowel disease patients.

BACKGROUND: The imbalance of commensal bacteria is called dysbiosis in intestinal microflora. Secreted IgA in the intestinal lumen plays an important role in the regulation of microbiota. Although dysbiosis of gut bacteria is reported in IBD patients, it remains unclear what makes dysbiosis of their microflora. The intervention method for remedy of dysbiosis in IBD patients is not well established. In this study, we focused on the quality of human endogenous IgA and investigated whether mouse monoclonal IgA which binds to selectively colitogenic bacteria can modulate human gut microbiota with IBD patients. METHODS: IgA-bound and -unbound bacteria were sorted by MACS and cell sorter. Sorted bacteria were analyzed by 16S rRNA sequencing to investigate what kinds of bacteria endogenous IgA or mouse IgA recognized in human gut microbiota. To evaluate the effect of mouse IgA, gnotobiotic mice with IBD patient microbiota were orally administrated with mouse IgA and analyzed gut microbiota. RESULTS: We show that human endogenous IgA has abnormal binding activity to gut bacteria in IBD patients. Mouse IgA can bind to human microbiota and bind to selectively colitogenic bacteria. The rW27, especially, has a growth inhibitory activity to human colitogenic bacteria. Furthermore, oral administration of mouse IgA reduced an inflammation biomarker, fecal lipocalin 2, in mice colonized with IBD patient-derived microbiota, and improved dysbiosis of IBD patient sample. CONCLUSION: Oral treatment of mouse IgA can treat gut dysbiosis in IBD patients by modulating gut microbiota.

Development of Orally Ingestible IgA Antibody Drugs to Maintain Symbiosis Between Humans and Microorganisms.

In recent years, dysbiosis, abnormalities in the gut microbiota, has been reported to be associated with the development of many diseases, and improving the gut microbiota is important for health maintenance. It has been shown that the host recognizes and regulates intestinal bacteria by means of IgA antibodies secreted into the gut, but the precise nature of the commensal gut bacteria recognized by each IgA antibody is unclear. We have cloned monoclonal IgA antibodies from mouse intestinal IgA-producing cells and are searching for bacterial molecules recognized by each IgA clone. Although the interaction of IgA antibodies with intestinal bacteria is still largely unknown and requires further basic research, we discuss the potential use of orally ingestible IgA antibodies as agents to improve intestinal microbiota.

MZB1-mediated IgA secretion suppresses the development and progression of colorectal cancer triggered by gut inflammation.

Colorectal cancer (CRC) ranks among the top causes of mortality globally. Gut inflammation is one crucial risk factor that augments CRC development since patients suffering from inflammatory bowel disease have an increased incidence of CRC. The role of immunoglobulin (Ig)A in maintaining gut homeostasis and preventing inflammation has been well established. Our earlier work demonstrated that the marginal zone and B1 cell-specific protein (MZB1) promotes gut IgA secretion and its absence results in pronounced dextran sulfate sodium salt (DSS)-induced colitis. In the present study, we explored the role of MZB1 in CRC development using the azoxymethane (AOM)/DSS-induced CRC model. We observed an increase in both the number and size of the tumor nodules in Mzb1-/- mice compared with Mzb1+/+ mice. The increase in CRC development and progression in Mzb1-/- mice was associated with reduced intestinal IgA levels, altered gut flora, and more severe gut and systemic inflammation. Oral administration of the monoclonal IgA, W27, alleviated both the gut inflammation and AOM/DSS-induced CRC. Notably, cohousing Mzb1+/+ and Mzb1-/- mice from the 10th day after birth led to similar CRC development. Our findings underscore the pivotal role of MZB1-mediated IgA secretion in suppressing the onset and progression of CRC triggered by gut inflammation. Moreover, our study highlights the profound impact of microbiota composition, modulated by gut IgA levels, on gut inflammation. Nonetheless, establishing a direct correlation between the severity of colitis and subsequent CRC development and the presence or absence of a particular microbiota is challenging.

Oral Corticosteroids Impair Mucin Production and Alter the Posttransplantation Microbiota in the Gut.

INTRODUCTION: Gut microbiota alterations cause inflammation in patients with ulcerative colitis (UC). Fecal microbiota transplantation (FMT) enables manipulating the microbiota's composition, but the mechanisms underlying colonization of the posttransplantation microbiota are poorly understood. METHODS: In this open-label, nonrandomized study, the FMT efficacy and changes in the gut microbiota were evaluated in 8 UC patients with mild-to-moderately active endoscopic colonic lesions. Compositional changes in the fecal and mucosal microbiotas between donors and recipients were examined via 16S rRNA-based sequencing. To investigate the effects of oral corticosteroids on microbiota colonization, FMT was performed in germ-free prednisolone (PSL)-administered mice to examine the factors determining colonization. RESULTS: Four UC patients achieved clinical remission (CR) after FMT, and 3 also achieved endoscopic remission. The fecal microbiotas of the CR patients changed similar to those of the donors after FMT. The mucin-coding gene, MUC2, was less expressed in the colons of the PSL-dependent patients than in the PSL-free patients. In the mice, PSL treatment decreased the fecal mucin production and altered the posttransplantation fecal microbiota composition. Adding either exogenous mucin or the mucin secretagogue, rebamipide, partially alleviated the PSL-induced dysbiosis of the gut microbiota. Administering rebamipide with FMT from healthy donors relieved inflammation in mice with Enterococcus faecium-induced colitis. CONCLUSION: Colonic mucin controlled the gut microbiota composition, and oral corticosteroid treatment modified the gut microbiota partly by reducing the colonic mucin.

Integrin CD11b provides a new marker of pre-germinal center IgA+ B cells in murine Peyer's patches.

Activated B cells can enter germinal centers (GCs) for affinity maturation to produce high-affinity antibodies. However, which activated B cells will enter GCs remains unknown. Here, we found a small population of CD11b+IgA+ B cells located outside of GCs in murine Peyer's patches (PPs). After injection of the CD11b+IgA+ PP B cells into a PP of a recipient mouse, they entered GCs forty hours later. They expressed GC surface markers and pre-GC B cell genes, suggesting that CD11b provides a novel surface marker of pre-GC IgA+ B cells in murine PPs. Furthermore, independently of dendritic cell activation, CD11b expression on B cells can be induced by bacterial antigens, such as pam3CSK4 and heat-killed Escherichia coli in vitro. In addition, mice orally administered with pam3CSK4 or heat-killed E. coli increased the number of PP GC B cells within two days, and enhanced the mucosal antigen-specific IgA response. Our results demonstrate that the induction of CD11b on B cells is a promising marker for selecting an effective mucosal vaccine adjuvant.

Therapeutic immunoglobulin A antibody for dysbiosis-related diseases.

Dysbiosis is alterations in the microbial composition compared with a healthy microbiota and often features a reduction in gut microbial diversity and a change in microbial taxa. Dysbiosis, especially in the gut, has also been proposed to play a crucial role in the pathogenesis of a wide variety of diseases, including inflammatory bowel disease, colorectal cancer, cardiovascular disease, obesity, diabetes and multiple sclerosis. A body of evidence has shown that intestinal polymeric immunoglobulin A (IgA) antibodies are important to regulate the gut microbiota as well as to exclude pathogenic bacteria or viral infection such as influenza and SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) at mucosal sites. Since the 1970s, trials for oral administration of therapeutic IgA or IgG have been performed mainly to treat infectious enteritis caused by pathogenic Escherichia coli or Clostridium difficile. However, few of them have been successfully developed for clinical application up to now. In addition to the protective function against intestinal pathogens, IgA is well known to modulate the gut commensal microbiota leading to symbiosis. Nevertheless, the development of therapeutic IgA drugs to treat dysbiosis is not progressing. In this review, the advantages of therapeutic IgA antibodies and the problems for their development will be discussed.

W27 IgA suppresses growth of Escherichia in an in vitro model of the human intestinal microbiota.

W27 monoclonal immunoglobulin A (IgA) suppresses pathogenic Escherichia coli cell growth; however, its effect on the human intestine remains unclear. We aimed to determine how W27 IgA affects the human colonic microbiota using the in vitro microbiota model. This model was established using fecal samples collected from 12 healthy volunteers; after anaerobic cultivation, each model was found to retain the genera found in the original human fecal samples. After pre-incubating W27 IgA with the respective fecal sample under aerobic conditions, the mixture of W27 IgA (final concentration, 0.5 µg/mL) and each fecal sample was added to the in vitro microbiota model and cultured under anaerobic conditions. Next-generation sequencing of the bacterial 16S rRNA gene revealed that W27 IgA significantly decreased the relative abundance of bacteria related to the genus Escherichia in the model. Additionally, at a final concentration of 5 µg/mL, W27 IgA delayed growth in the pure culture of Escherichia coli isolated from human fecal samples. Our study thus revealed the suppressive effect of W27 IgA on the genus Escherichia at relatively low-concentrations and the usefulness of an in vitro microbiota model to evaluate the effect of IgA as a gut microbiota regulator.

Functional production of human antibody by the filamentous fungus Aspergillus oryzae.

BACKGROUND: Monoclonal antibodies (mAbs) as biopharmaceuticals take a pivotal role in the current therapeutic applications. Generally mammalian cell lines, such as those derived from Chinese hamster ovaries (CHO), are used to produce the recombinant antibody. However, there are still concerns about the high cost and the risk of pathogenic contamination when using mammalian cells. Aspergillus oryzae, a filamentous fungus recognized as a GRAS (Generally Regarded As Safe) organism, has an ability to secrete a large amount of proteins into the culture supernatant, and thus the fungus has been used as one of the cost-effective microbial hosts for heterologous protein production. Pursuing this strategy the human anti-TNFα antibody adalimumab, one of the world's best-selling antibodies for the treatment of immune-mediated inflammatory diseases including rheumatoid arthritis, was chosen to produce the full length of mAbs by A. oryzae. Generally, N-glycosylation of the antibody affects immune effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC) via binding to the Fc receptor (FcγR) on immune cells. The CRISPR/Cas9 system was used to first delete the Aooch1 gene encoding a key enzyme for the hyper-mannosylation process in fungi to investigate the binding ability of antibody with FcγRIIIa. RESULTS: Adalimumab was expressed in A. oryzae by the fusion protein system with α-amylase AmyB. The full-length adalimumab consisting of two heavy and two light chains was successfully produced in the culture supernatants. Among the producing strains, the highest amount of antibody was obtained from the ten-protease deletion strain (39.7 mg/L). Two-step purifications by Protein A and size-exclusion chromatography were applied to obtain the high purity sample for further analysis. The antigen-binding and TNFα neutralizing activities of the adalimumab produced by A. oryzae were comparable with those of a commercial product Humira®. No apparent binding with the FcγRIIIa was detected with the recombinant adalimumab even by altering the N-glycan structure using the Aooch1 deletion strain, which suggests only a little additional activity of immune effector functions. CONCLUSION: These results demonstrated an alternative low-cost platform for human antibody production by using A. oryzae, possibly offering a reasonable expenditure for patient's welfare.

MZB1 promotes the secretion of J-chain-containing dimeric IgA and is critical for the suppression of gut inflammation.

IgA is the most abundantly produced antibody in the body and plays a crucial role in gut homeostasis and mucosal immunity. IgA forms a dimer that covalently associates with the joining (J) chain, which is essential for IgA transport into the mucosa. Here, we demonstrate that the marginal zone B and B-1 cell-specific protein (MZB1) interacts with IgA through the α-heavy-chain tailpiece dependent on the penultimate cysteine residue and prevents the intracellular degradation of α-light-chain complexes. Moreover, MZB1 promotes J-chain binding to IgA and the secretion of dimeric IgA. MZB1-deficient mice are impaired in secreting large amounts of IgA into the gut in response to acute inflammation and develop severe colitis. Oral administration of a monoclonal IgA significantly ameliorated the colitis, accompanied by normalization of the gut microbiota composition. The present study identifies a molecular chaperone that promotes J-chain binding to IgA and reveals an important mechanism that controls the quantity, quality, and function of IgA.

Decreased Taxon-Specific IgA Response in Relation to the Changes of Gut Microbiota Composition in the Elderly.

Gut microbiota is known to change with aging; however, the underlying mechanisms have not been well elucidated. Immunoglobulin A (IgA) is the dominant class of antibody secreted by the intestinal mucosa, and are thought to play a key role in the regulation of the gut microbiota. T cells regulate the magnitude and nature of microbiota-specific IgA responses. However, it is also known that T cells become senescent in elderly people. Therefore, we speculated that the age-related changes of IgA response against the gut microbiota might be one of the mechanisms causing the age-associated changes of gut microbiota composition. To prove our hypothesis, fecal samples from 40 healthy subjects (adult group: n = 20, an average of 35 years old; elderly group: n = 20, an average of 76 years old) were collected, and the gut microbiota composition and the response of IgA to gut microbiota were investigated. The relative abundance of Bifidobacteriaceae was significantly lower, whereas those of Clostridiaceae, Clostridiales;f__ and Enterobacteriaceae were significantly higher in the elderly group than in the adult group. There was no significant difference in the fecal IgA concentration between the adult and elderly groups. However, the taxon-specific IgA response to some bacterial taxa was different between the adult and elderly groups. To evaluate inter-group differences in the taxon-specific IgA response to each bacterial taxon, the IgA-indices were calculated, and the IgA-indices of Clostridiaceae and Enterobacteriaceae were found to be significantly lower in the elderly group than the adult group. In addition, Clostridiales;f__ and Enterobacteriaceae were significantly enriched in the IgA+ fraction in the adult group but not in the elderly group, whereas Clostridiaceae was significantly enriched in the IgA- fraction in the elderly group but not in the adult group. Some species assigned to Clostridiaceae or Enterobacteriaceae are known to be pathogenic bacteria. Our results suggest the possible contribution of decreased IgA response in the increased abundance of bacterial taxa with potential pathogenicity in the intestinal environment of the elderly. Our findings contribute to the understanding of the regulatory factor for the changes in the gut microbiota composition with aging.

Accelerated Systemic Autoimmunity in the Absence of Somatic Hypermutation in 564Igi: A Mouse Model of Systemic Lupus with Knocked-In Heavy and Light Chain Genes.

564Igi mice have knocked-in immunoglobulin (Ig) heavy (H) and light (L) chain genes that encode an autoantibody recognizing RNA. Previously, we showed that these mice produce pathogenic IgG autoantibodies when activation-induced deaminase (AID) is expressed in pre-B and immature B cells but not when it is expressed only in mature B cells. AID has two functions; it is necessary for somatic hypermutation (SHM) and class switch recombination (CSR). To determine the role of each of these functions in the generation of pathogenic autoantibodies, we generated 564Igi mice that carry a mutant AID-encoding gene, Aicda (AicdaG23S), which is capable of promoting CSR but not SHM. We found that 564Igi AicdaG23S mice secreted class-switched antibodies (Abs) at levels approximately equal to 564Igi mice. However, compared to 564Igi mice, 564Igi Aicda G23S mice had increased pathogenic IgG Abs and severe systemic lupus erythematosus-like disease, including, glomerulonephritis, and early death. We suggest that in 564Igi mice SHM by AID changes Ig receptors away from self reactivity, thereby mitigating the production of autoantibody, providing a novel mechanism of tolerance.

Intestinal IgA as a modulator of the gut microbiota.

Accumulating evidence suggests that dysbiosis plays a role in the pathogenesis of intestinal diseases including inflammatory bowel disease (IBD) as well as extra-intestinal disorders. As a modulator of the intestinal microbiota, we isolated a mouse monoclonal IgA antibody (clone W27) with high affinities for multiple commensal bacteria, but not for beneficial bacteria such as Lactobacillus casei (L. casei). Via specific recognition of an epitope in serine hydroxymethyltransferase (SHMT), a bacterial metabolic enzyme, W27 IgA selectively inhibited the in vitro growth of bound bacteria, including Escherichia coli (E. coli), while having no effect on unbound beneficial bacteria such as L. casei. By modulating the gut microbiota in vivo, oral administration of W27 IgA effectively prevented development of colitis in several mouse models. Here we discuss how intestinal IgA modulates the gut microbiota through recognition of SHMT.

High-affinity monoclonal IgA regulates gut microbiota and prevents colitis in mice.

Immunoglobulin A (IgA) is the main antibody isotype secreted into the intestinal lumen. IgA plays a critical role in the defence against pathogens and in the maintenance of intestinal homeostasis. However, how secreted IgA regulates gut microbiota is not completely understood. In this study, we isolated monoclonal IgA antibodies from the small intestine of healthy mouse. As a candidate for an efficient gut microbiota modulator, we selected a W27 IgA, which binds to multiple bacteria, but not beneficial ones such as Lactobacillus casei. W27 could suppress the cell growth of Escherichia coli but not L. casei in vitro, indicating an ability to improve the intestinal environment. Indeed W27 oral treatment could modulate gut microbiota composition and have a therapeutic effect on both lymphoproliferative disease and colitis models in mice. Thus, W27 IgA oral treatment is a potential remedy for inflammatory bowel disease, acting through restoration of host-microbial symbiosis.

A novel germline mutation in a patient with nevoid basal cell carcinoma syndrome showing cystic lesion in the lung.

Nevoid basal cell carcinoma syndrome (NBCCS) manifests multiple defects involving the skin, endocrine and nervous systems, eyes and bones. Mutations in the patched homologue 1 (PTCH1) gene are the underlying causes of NBCCS, leading to aberrant cell proliferation through constitutive activation of the hedgehog signaling pathway. We identified a novel frameshift mutation (c.1207dupT) of PTCH1 in a NBCCS patient, which might explain multiple cystic lesions and neoplastic growth in the patient.

Myelin basic protein as a novel genetic risk factor in rheumatoid arthritis--a genome-wide study combined with immunological analyses.

Rheumatoid arthritis (RA) is a major cause of adult chronic inflammatory arthritis and a typical complex trait. Although several genetic determinants have been identified, they account for only a part of the genetic susceptibility. We conducted a genome-wide association study of RA in Japanese using 225,079 SNPs genotyped in 990 cases and 1,236 controls from two independent collections (658 cases and 934 controls in collection1; 332 cases and 302 controls in collection2), followed by replication studies in two additional collections (874 cases and 855 controls in collection3; 1,264 cases and 948 controls in collection4). SNPs showing p<0.005 in the first two collections and p<10(-4) by meta-analysis were further genotyped in the latter two collections. A novel risk variant, rs2000811, in intron2 of the myelin basic protein (MBP) at chromosome 18q23 showed strong association with RA (p = 2.7×10(-8), OR 1.23, 95% CI: 1.14-1.32). The transcription of MBP was significantly elevated with the risk allele compared to the alternative allele (p<0.001). We also established by immunohistochemistry that MBP was expressed in the synovial lining layer of RA patients, the main target of inflammation in the disease. Circulating autoantibody against MBP derived from human brain was quantified by ELISA between patients with RA, other connective tissue diseases and healthy controls. As a result, the titer of anti-MBP antibody was markedly higher in plasma of RA patients compared to healthy controls (p<0.001) and patients with other connective tissue disorders (p<0.001). ELISA experiment using citrullinated recombinant MBP revealed that a large fraction of anti-MBP antibody in RA patients recognized citrullinated MBP. This is the first report of a genetic study in RA implicating MBP as a potential autoantigen and its involvement in pathogenesis of the disease.

Histone chaperone Spt6 is required for class switch recombination but not somatic hypermutation.

Activation-induced cytidine deaminase (AID) is shown to be essential and sufficient to induce two genetic alterations in the Ig loci: class switch recombination (CSR) and somatic hypermutation (SHM). However, it is still unknown how a single-molecule AID differentially regulates CSR and SHM. Here we identified Spt6 as an AID-interacting protein by yeast two-hybrid screening and immunoprecipitation followed by mass spectrometry. Knockdown of Spt6 resulted in severe reduction of CSR in both the endogenous Ig locus in B cells and an artificial substrate in fibroblast cells. Conversely, knockdown of Spt6 did not reduce but slightly enhanced SHM in an artificial substrate in B cells, indicating that Spt6 is required for AID to induce CSR but not SHM. These results suggest that Spt6 is involved in differential regulation of CSR and SHM by AID.

Mice carrying a knock-in mutation of Aicda resulting in a defect in somatic hypermutation have impaired gut homeostasis and compromised mucosal defense.

To elucidate the specific role of somatic hypermutation (SHM) in mucosal immunity, we generated mice carrying a knock-in point mutation in Aicda, which encodes activation-induced cytidine deaminase (AID), an enzyme essential to SHM and class-switch recombination (CSR). These mutant AID(G23S) mice had much less SHM but had normal amounts of immunoglobulin in both serum and intestinal secretions. AID(G23S) mice developed hyperplasia of germinal center B cells in gut-associated lymphoid tissues, accompanied by expansion of microflora in the small intestine. Moreover, AID(G23S) mice had more translocation of Yersinia enterocolitica into mesenteric lymph nodes and were more susceptible than wild-type mice to oral challenge with cholera toxin. Together our results indicate that SHM is critical in maintaining intestinal homeostasis and efficient mucosal defense.