A PATHOGEN-SPECIFIC EPITOPE INSERTED INTO RECOMBINANT SECRETORY IMMUNOGLOBULIN-A IS IMMUNOGENIC BY THE ORAL ROUTE

Oral administration of rabbit secretory IgA (sIgA) to adult BALB/c mic e induced IgA(+), IgM(+), and IgG(+) lymphoblasts in the Peyer's patch es, whose fusion with myeloma cells resulted in hybridomas producing I gA, IgM, and IgG1 antibodies to the secretory component (SC). This sug gests that SC could serve as a vector to target protective epitopes in to mucosal lymphoid tissue and elicit an immune response. We tested th is 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 const ructed a molecular model of the first and second Ig-like domains of ra bbit SC. A surface epitope recognized by an SC-specific antibody was m apped to the loop connecting the E and F beta strands of domain I. Thi s 8-amino acid sequence was replaced by a 9-amino acid linear epitope from S. flexneri invasin B. We found that cellular trafficking of reco mbinant SC produced in mammalian CV-1 cells was drastically altered an d resulted in a 50-fold lower rate of secretion, However, purification of chimeric SC could be achieved by Ni2+-chelate affinity chromatorap hy. Both wild type and chimeric SC bound to dimeric IgA, but not to mo nomeric 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 response s.