Secretory immunoglobulin a heavy chain presents Gal beta 1-3GalNAc bindingstructures for Actinomyces naeslundli genospecies 1

Adherence of Actinomyces naeslundii ATCC 12104 to hydroxyapatite beads coat ed with protein fractions of parotid saliva, obtained by gel filtration on S-200 HX columns, showed GalNAc beta 1-3Gal alpha-O-ethyl-inhibitable bindi ng to high-molecular-weight proteins (Stromberg et al., 1992). The present study investigates the nature of these high-molecular-weight binding protei ns and determines their specific ability to mediate adherence to representa tive strains of Actinomyces species. Strain ATCC 12104 bound specifically i n a lactose-inhibitable manner to the heavy chain of secretory immunoglobul in A (S-IgA), contained within a high-molecular-weight parotid protein frac tion separated on SDS-PAGE and transferred to a solid membrane support. Lac tose-inhibitable binding to the heavy chain of S-IgA from human colostrum w as also demonstrated. Peanut agglutinin bound to the heavy chain of parotid and colostrum S-IgAs contained on solid support membranes, confirming the presence of Gal beta 1-3GalNAc residues on these molecules. Both salivary a nd colostrum S-IgA aggregated with strain ATCC 12104 in a GalNAc beta 1-3Ga l alpha-O-ethyl-inhibitable fashion. Further separation of high-molecular-w eight salivary proteins on 5-500 HX columns showed GalAc beta 1-3Gal alpha- O-ethyl-inhibitable binding to both mucin- and S-IgA-containing fractions. The presence of S-IgA in salivary pellicles formed in vivo on teeth was dem onstrated by Western blot analysis of pellicle extracts with anti-IgA antib odies. Among strains representing A. naeslundii genospecies 1 and 2 and A. odontolyticus, only those of genospecies 1 with a particular adherence prof ile showed efficient GalNAc beta 1-3Gal alpha-O-ethyl-inhibitable binding t o S-IgA. Thus, oligosaccharides on S-IgA may promote bacterial aggregation (or adherence) and provide a mechanism by which S-IgA can interact with bac teria without prior immunological challenge.