The Compromised Mucosal Immune System of β7 Integrin-Deficient Mice Has Only Minor Effects on the Fecal Microbiota in Homeostasis

The Underappreciated Role of Secretory IgA in IBD

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

Antibody secreting cells are critically dependent on integrin α4β7/MAdCAM-1 for intestinal recruitment and control of the microbiota during chronic colitis

T and B cells employ integrin α4β7 to migrate to intestine under homeostatic conditions. Whether those cells differentially rely on α4β7 for homing during inflammatory conditions has not been fully examined. This may have implications for our understanding of the mode of action of anti-integrin therapies in inflammatory bowel disease (IBD). Here, we examined the role of α4β7 integrin during chronic colitis using IL-10^-/- mice, β7-deficient IL-10^-/-, IgA-deficient IL-10^-/- mice, and antibody blockade of MAdCAM-1. We found that α4β7 was predominantly expressed by B cells. β7 deficiency and MAdCAM-1 blockade specifically depleted antibody secreting cells (ASC) (not T cells) from the colonic LP, leading to a fecal pan-immunoglobulin deficit, severe colitis, and alterations of microbiota composition. Colitis was not due to defective regulation, as dendritic cells (DC), regulatory T cells, retinaldehyde dehydrogenase (RALDH) expression, activity, and regulatory T/B-cell cytokines were all comparable between the strains/treatment. Finally, an IgA deficit closely recapitulated the clinical phenotype and altered microbiota composition of β7-deficient IL-10^-/- mice. Thus, a luminal IgA deficit contributes to accelerated colitis in the β7-deficient state. Given the critical/nonredundant dependence of IgA ASC on α4β7:MAdCAM-1 for intestinal homing, B cells may represent unappreciated targets of anti-integrin therapies.

The biological regulatory activities of Flammulina velutipes polysaccharide in mice intestinal microbiota, immune repertoire and heart transcriptome

The effects of a novel Flammulina velutipes polysaccharide (FVP) on intestinal microbiota, immune repertoire and heart transcriptome were investigated in this study. The results showed that FVP treatment could effectively regulate the abundance of colonic microbiota. And FVP exhibited obvious immunoregulatory effect by influencing V gene and J gene fragments usage on TCRα chain. The usage frequency of TRBV1, TRBJ1-6 and TRBJ1-5 were significantly altered, and 41 V-J pairs were identified with obvious difference after FVP treatment. Furthermore, the mRNA of mice heart was analyzed by transcriptome assay. Total 525 genes and 1587 mRNA were significantly changed after FVP treatment. KEGG annotation indicated that the up-regulated mRNA was enriched in 17 pathways including adherens junction, mTOR signaling pathway, insulin signaling pathway, mitophagy, tight junction, PPAR signaling pathway and TNF signaling pathway, etc. Meanwhile, the down-regulated mRNA was gathered in AMPK signaling pathway, metabolism of xenobiotics by cytochrome P450, apelin signaling pathway, PPAR signaling pathway, PI3K-Akt signaling pathway, insulin signaling pathway, cardiac muscle contraction, adrenergic signaling in cardiomyocytes, Fc gamma R-mediated phagocytosis, etc. The great potential exhibited by FVP could make it an ideal candidate as complementary medicine or functional food for promotion of health.

An integrin αEβ7-dependent mechanism of IgA transcytosis requires direct plasma cell contact with intestinal epithelium

Efficient IgA transcytosis is critical for the maintenance of a homeostatic microbiota. In the canonical model, locally-secreted dimeric (d)IgA reaches the polymeric immunoglobulin receptor (pIgR) on intestinal epithelium via simple diffusion. A role for integrin αE(CD103)β7 during transcytosis has not been described, nor its expression by intestinal B cell lineage cells. We found that αE-deficient (αE^-/-) mice have a luminal IgA deficit, despite normal antibody-secreting cells (ASC) recruitment, local IgA production and increased pIgR expression. This deficit was not due to dendritic cell (DC)-derived retinoic acid (RA) nor class-switching defects, as stool from RAG^-/- mice reconstituted with αE^-/- B cells was also IgA deficient. Flow cytometric, ultrastructural and transcriptional profiling showed that αEβ7-expressing ASC represent an undescribed subset of terminally-differentiated intestinal plasma cells (PC) that establishes direct cell to cell contact with intestinal epithelium. We propose that IgA not only reaches pIgR through diffusion, but that αEβ7+ PC dock with E-cadherin-expressing intestinal epithelium to directly relay IgA for transcytosis into the intestinal lumen.

Ascorbic Acid Derivative 2-O-β-d-Glucopyranosyl-l-Ascorbic Acid from the Fruit of Lycium barbarum Modulates Microbiota in the Small Intestine and Colon and Exerts an Immunomodulatory Effect on Cyclophosphamide-Treated BALB/c Mice

2-O-β-d-Glucopyranosyl-l-ascorbic acid (AA-2βG) is a natural and stable ascorbic acid derivative isolated from the fruits of Lycium barbarum. In our present study, cyclophosphamide (Cy) was used to make BALB/c mice immunosuppressive and AA-2βG was used to intervene immunosuppressive mice. It was found that Cy treatment resulted in a series of changes on basic immune indexes including a decrease of thymus and spleen indexes and levels of pro-inflammatory cytokines and destruction of leucocyte proportion balance, accompanied with weight loss, reduction in colon length, and changes of hepatic function markers. However, all these changes were reversed in varying degrees by AA-2βG intervention. Notably, AA-2βG could significantly change both mouse colonic and small-intestinal microbiota. The key responsive taxa found in a mouse colon were Muribaculaceae, Ruminococcaceae, Oscillibacter, Rikenella, Helicobacter, Negativibacillus, Alistipes, and Roseburia, and the key responsive taxa found in a mouse small intestine were Muribaculaceae, Anaerotruncus, and Paenibacillus. The results demonstrated that AA-2βG could modulate microbiota in the small intestine and colon and exert an immunomodulatory effect. Further studies should focus on the degradation pathways of AA-2βG and the interaction between AA-2βG and Muribaculaceae.