EFFECT OF IGA1 PROTEASE ON THE ABILITY OF SECRETORY IGA1 ANTIBODIES TO INHIBIT THE ADHERENCE OF STREPTOCOCCUS-MUTANS

Secretory IgA (SIgA) is the principal immunoglobulin isotype present i n the mucosal secretions of humans. SIgA is thought to play a major ro le in host defense at these surfaces by inhibiting the colonization of potentially pathogenic microorganisms. A number of bacteria that are mucosal pathogens of humans produce a protease that specifically cleav es the IgA1 subclass of humans and great apes at the hinge region to p roduce Fab and Fc fragments. In order to study the effect of IgA1 prot ease on the ability of SIgA1 antibodies to inhibit bacterial adherence , an in vitro assay that quantifies the adsorption of radiolabeled Str eptococcus mutans to hydroxyapatite (HA) beads was employed. High tite r S. mutans-specific SIgA1 and SIgA2 antibodies were induced in chimpa nzee milk for use in the assay. Fab alpha 1 fragments had significantl y reduced ability to inhibit adherence of S. mutans to saliva-coated H A compared to intact SIgA1 or SIgA2 anti-S, mutans antibodies. These d ata support the potential importance of IgA1 proteases as an ecologica l determinant in the oral cavity and their role as a determinant of pa thogenesis of pathogenic bacteria whose portal of entry is the mucosal surface.