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 IgAl Protease Cleavage

The effect of human secretory immunoglobulin A (S-IgA) and serum antibodies to surface protein antigen (Ag) 1I/ on the adherence of Ag VII-bearing Streptococcus mutans and of free Ag VII to saliva-coated hydroxyapatite (SHA) was investigated. The inhibition by S-IgA of binding of both S. mutans and free Ag IJI to SHA was dependent on antibody to Ag VII. Essentially no difference was found between S-IgAl and S-IgA2 with respect to antibody-dependent inhibition of Ag I/II binding to SHA, but S-IgAl inhibited S. mutans adherence more effectively than did either serum immunoglobulin Al (IgAl) or IgG antibodies. The antiadherence effect of S-IgA was abrogated after cleavage by IgAl protease. Purified Faba fragments containing Ag I/I-binding activity enhanced the binding of free Ag I/I to SHA and showed greater binding to SHA than did intact S-IgAl. Despite its relative inability to interact with precoated SHA, S-IgAl containing antibody to Ag I/I was readily incorporated into the salivary pellicle during coating, but this did not promote Ag I/I 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 IgAl proteases would potentially interfere with this antiadherence mechanism.