Secretory IgA's complex roles in immunity and mucosal homeostasis in the gut

Abstract

Secretory IgA (SIgA) serves as the first line of defense in protecting the intestinal epithelium from enteric toxins and pathogenic microorganisms. Through a process known as immune exclusion, SIgA promotes the clearance of antigens and pathogenic microorganisms from the intestinal lumen by blocking their access to epithelial receptors, entrapping them in mucus, and facilitating their removal by peristaltic and mucociliary activities. In addition, SIgA functions in mucosal immunity and intestinal homeostasis through mechanisms that have only recently been revealed. In just the past several years, SIgA has been identified as having the capacity to directly quench bacterial virulence factors, influence the composition of the intestinal microbiota by Fab-dependent and -independent mechanisms, promote the retro-transport of antigens across the intestinal epithelium to dendritic cell (DC) subsets in gut-associated lymphoid tissue, and, finally, to down-regulate pro-inflammatory responses normally associated with the uptake of highly pathogenic bacteria and potentially allergenic antigens. This review summarizes the intrinsic biological activities now associated with SIgA and their relationships to immunity and intestinal homeostasis.

Human Plasma-derived Polymeric IgA and IgM Antibodies Associate with Secretory Component to Yield Biologically Active Secretory-like Antibodies

“…antibiotics, anti-virals, and IgG). Importantly, the combination of two crucial functional properties, namely antigen recognition via Fab (similar to IgG), and anti-inflammatory effector function via Fc is an additional argument to consider IgA in prevention/treatment of mucosal infection and particularly of inflammation associated with chronic infection (45)(46)(47). Starting from 1 liter of plasma, current purification procedures allow to recover 40 -50 mg of J chain-containing pIgA and up to 100 mg of IgM.…”

Re-thinking the functions of IgA+plasma cells

“…IgA entraps Ag and affects microbial virulence within cells and the mucus and prevents binding to cells and dissemination. 12,[76][77][78][79] IgA has been shown to bind to several receptors including FcaRI (CD89), transferrin receptor (CD71), a receptor for the secretory component, Galectin-1 and a microfold-cell IgA receptor, all of which have distinct expression patterns on myeloid, lymphoid or non-haematopoietic cells. 6 Interaction of the Fc region of IgA with its receptors instructs and regulates intestinal innate and adaptive immunity through regulation of cellular functions upon ligation of IgA receptors.…”

Serum Anti-Vibrio cholerae Immunoglobulin Isotype in BALB/c Mice Immunized With ompW-Loaded Chitosan

“…Infection with Vibrio cholerae (V. cholerae) results in widespread responses, from serologic to acute purging, and recovery from the infection depends on elimination of the V. cholerae bacteria by antibiotics or the patient's own immune response (2). Presence of specific antibodies against the bacteria or the cholera toxin or both of them in the circulation usually induce a resistance to infection (3). The outer membrane protein W (ompW) of V. cholerae is expected to stimulate the immune response and induce protective immunity in the host (4,5).…”