Glycans on Secretory Component Participate in Innate Protection against Mucosal Pathogens

Abstract

In mucosal secretions, secretory component (SC) is found either free or bound to polymeric IgA within the secretory IgA complex. SC displays numerous and various glycans, which are potential ligands for bacterial compounds. We first established that human SC (hSC) purified from colostrum (hSCcol) or produced in Chinese hamster ovary cells (hSCrec) exhibits the same lectin reactivity. Both forms bind to Clostridium difficile toxin A and functionally protect polarized Caco-2 cell monolayers from the cytopathic effect of the toxin. The interaction is mediated by glycans present on hSC and involves galactose and sialic acid residues. hSCcol and hSCrec were also shown to bind enteropathogenic Escherichia coli adhesin intimin and to inhibit its infectivity on HEp-2 cells in a glycan-dependent manner as well. SC remained operative in the context of the whole secretory IgA molecule and can therefore enhance its Fabmediated neutralizing properties. On the contrary, hSC did not interact with three different strains of rotavirus (RF, RRV, and SA11). Accordingly, infection of target MA104 cells with these rotavirus strains was not reduced in the presence of either form of hSC tested. Although not a universal mechanism, these findings identify hSC as a microbial scavenger contributing to the antipathogenic arsenal that protects the body epithelial surfaces.

Reconstituted Human Polyclonal Plasma-derived Secretory-like IgM and IgA Maintain the Barrier Function of Epithelial Cells Infected with an Enteropathogen

“…However, in vivo, the presence of bound SC is essential for the stability and anchoring of the molecule at mucosal surfaces (3). Furthermore, in addition to interfering with bacterial targeting of epithelial cells via carbohydrates abundantly found on its surface (44), SC associated with pIgA and IgM appears to intervene negatively in the secretion of S. flexneri virulence factors crucial for the infection of epithelial cells (45,46). These results suggest the unexpected role of polyclonal SIgA and SIgM mostly in altering bacterial metabolism, which adds to recognized mechanisms of protection effective at the level of the mucosal epithelium.…”

Recognition of Gram-positive Intestinal Bacteria by Hybridoma- and Colostrum-derived Secretory Immunoglobulin A Is Mediated by Carbohydrates

“…These data are in sharp contrast with our results obtained with the nonpathogenic E. coli commensal strains D2241 and Nissle for which maintenance of binding could be observed following SC deglycosylation. Because only pathogenic E. coli strains including enteropathogenic E. coli express outer membrane intimin (46) involved in the interaction with glycans present on SC (24), this may explain differences in SIgA binding. The sum of these data implies that the Fab-and Fc-independent molecular features responsible for bacterial coating are highly plastic and flexible and result in diverse biological consequences.…”

“…2A). The shift of the apparent molecular mass from 80 kDa down to 62-65 kDa is indicative of fully deglycosylated SC (24). In contrast, carbohydrate moieties present on the ␣ chain were insensitive to the action of the enzyme, suggesting a nonaccessible anchoring of the carbohydrates in pIgA (Fig.…”

Antigen Binding to Secretory Immunoglobulin A Results in Decreased Sensitivity to Intestinal Proteases and Increased Binding to Cellular Fc Receptors

“…100 ng of C. difficile toxin A was mixed with 50 ng of either pIgAPCG-4 or SIgAPCG-4 permitting neutralization in in vitro assays (11). 60 ng of purified rotavirus was incubated with 100 ng of either pIgA7D9 or SIgA7D9 in PBS for 2 h at room temperature, corresponding to ϳ160 Ab molecules/virus (19). 10 8 S. flexneri were incubated with 120 ng of either pIgAC5 or SIgAC5 in PBS for 25 min on ice, corresponding to ϳ2000 Ab molecules/bacterium (20).…”

“…Virus titer present in the lysed cell supernatants was determined by plaque assay and expressed as plaque-forming units/ml. The virus was purified on a cesium chloride gradient as described before (19) and conserved at 4°C until further use. For biochemical analyses, purified rotavirus solutions were desalted immediately before use by gel filtration on Sephadex G-25 coarse beads (Amersham Biosciences), and the concentration was calculated by spectrophotometry (Ultrospec 300; Pharmacia Biotech) using the following correlation: 5.3 A 260 corresponds to 1 mg/ml virus.…”