A Pathogen-specific Epitope Inserted into Recombinant Secretory Immunoglobulin A Is Immunogenic by the Oral Route

Abstract

Oral administration of rabbit secretory IgA (sIgA) to adult BALB/c mice induced IgA ؉ , IgM ؉ , and IgG ؉ lymphoblasts in the Peyer's patches, whose fusion with myeloma cells resulted in hybridomas producing IgA, IgM, and IgG1 antibodies to the secretory component (SC). This suggests that SC could serve as a vector to target protective epitopes into mucosal lymphoid tissue and elicit an immune response. We tested this concept by inserting a Shigella flexneri invasin B epitope into SC, which, following reassociation with IgA, was delivered orally to mice. To identify potential insertion sites at the surface of SC, we constructed a molecular model of the first and second Ig-like domains of rabbit SC. A surface epitope recognized by an SC-specific antibody was mapped to the loop connecting the E and F ␤ strands of domain I. This 8-amino acid sequence was replaced by a 9-amino acid linear epitope from S. flexneri invasin B. We found that cellular trafficking of recombinant SC produced in mammalian CV-1 cells was drastically altered and resulted in a 50-fold lower rate of secretion. However, purification of chimeric SC could be achieved by Ni 2؉ -chelate affinity chromatoraphy. Both wild-type and chimeric SC bound to dimeric IgA, but not to monomeric IgA. Reconstituted sIgA carrying the invasin B epitope within the SC moiety triggers the appearance of seric and salivary invasin B-specific antibodies. Thus, neo-antigenized sIgA can serve as a mucosal vaccine delivery system inducing systemic and mucosal immune responses.

Mapping the Interaction Between Murine IgA and Murine Secretory Component Carrying Epitope Substitutions Reveals a Role of Domains II and III in Covalent Binding to IgA

“…In conclusion, we present evidence that surface loops in domains II and III of mSC do not affect binding to IgA d , in contrast to what was observed for the same loops in domain I (5,27). Antibody reactivity of the FLAG motif in domains II and III loops in free and IgA d -bound mSC mutants maps multiple insertion sites for epitope substitution.…”

“…Wild type mSC and mSC-FLAG mutants were selective for IgA d over IgA m , as was our mutant of loop E-F in rabbit SC (27). Recombinant hSC domain I was shown to bind IgA m but not IgG (18), suggesting that this domain discriminates among Ig classes, whereas the other domains are responsible for distinguishing the oligomeric state of the Ig.…”

Selective Adherence of IgA to Murine Peyer’s Patch M Cells: Evidence for a Novel IgA Receptor

“…There is current interest in targeting vaccines to the apical surfaces of M cells in the human small intestine, colon, and rectum. In mice, exogenous IgA has been used as an Ag delivery vehicle, apparently promoting the sampling of oral or rectal vaccines by M cells and more efficient delivery to the mucosal immune system (45,46). A better understanding of the interaction of SIgA with M cells and the resulting immune response is needed to assess the feasibility of such a vaccine strategy in humans.…”

Roundtrip Ticket for Secretory IgA: Role in Mucosal Homeostasis?

“…To address the issue of whether transport of SIgA Ab across the M cell could trigger immune responses, rabbit SC was genetically engineered to deliver in association with pIgA a foreign epitope from Shigella flexneri invasin B to the intestinal lymphoid tissue (58). Oral administration to mice of the "antigenized" SIgA in the presence of cholera toxin evoked immune responses that included Abs against both invasin B and the SC carrier.…”