Interference of secretory immunoglobulin A with sorption of oral bacteria to hydroxyapatite

Abstract

The potential of secretory IgA (S-IgA) to interfere with the initial phase of dental plaque formation was studied by using an in vitro method which permits the quantitative determination of the sorption of radiolabeled oral bacterial cells to hydroxyapatite (HA) beads. The importance of specific S-IgA antibodies was evaluated by a comparison of the effect of pure preparations of colostral S-IgA, polymeric myeloma IgA or preabsorbed S-IgA. Specific antibody molecules bound at the HA surface significantly enhanced the sorption of 2 Streptococcus sanguis strains. HA-bound S-IgA antibodies inhibited the sorption of S. mitior and S. salivarius. The same was true for S. mutans cells but only when they were propagated in the absence of sucrose. Suspended in saliva, cells of all streptococcal species adhered in significantly lower numbers to HA. Comparative experiments with bacteria suspended in solutions of various preparations of IgA or Ig-deficient salivas with S-IgA or myeloma IgA added indicated that the adherence inhibition seen with S. sanguis, S. mitior, S. salivarius and glucose-grown S. mutans was partly attributable to functions of S-IgA antibodies. Under the in vitro conditions of the study, S-IgA antibodies had no effect on the sorption of sucrose-grown S. mutans, Actinomyces viscosus and A. naeslundii to HA. S-IgA can interfere with the sorption of some oral bacteria to HA by several different functions.