Inhibition of Streptococcus mutans adherence to saliva-coated hydroxyapatite by human secretory immunoglobulin A (S-IgA) antibodies to cell surface protein antigen I/II: reversal by IgA1 protease cleavage.

The effect of human secretory immunoglobulin A (S-IgA) and serum antibodies to surface protein antigen (Ag) I/II on the adherence of Ag I/II-bearing Streptococcus mutans and of free Ag I/II to saliva-coated hydroxyapatite (SHA) was investigated. The inhibition by S-IgA of binding of both S. mutans and free Ag I/II to SHA was dependent on antibody to Ag I/II. Essentially no difference was found between S-IgA1 and S-IgA2 with respect to antibody-dependent inhibition of Ag I/II binding to SHA, but S-IgA1 inhibited S. mutans adherence more effectively than did either serum immunoglobulin A1 (IgA1) or IgG antibodies. The antiadherence effect of S-IgA was abrogated after cleavage by IgA1 protease. Purified Fab alpha fragments containing Ag I/II-binding activity enhanced the binding of free Ag I/II to SHA and showed greater binding to SHA than did intact S-IgA1. Despite its relative inability to interact with precoated SHA, S-IgA1 containing antibody to Ag I/II was readily incorporated into the salivary pellicle during coating, but this did not promote Ag I/II binding. These data suggest that S-IgA antibodies can inhibit the initial adherence of S. mutans to salivary pellicle-coated tooth surfaces in an adhesin-specific fashion, but the presence in the oral cavity of bacterial IgA1 proteases would potentially interfere with this antiadherence mechanism.