Detection of Immunoglobulin Al Protease - Induced Fab , Fragments on Dental Plaque Bacteria

The mechanisms by which immunoglobulin Al (IgAl) protease activity may enable bacteria to evade the effect of specific secretory IgA (S-IgA) antibodies are not clear. A possibility which has received indirect experimental support is that bacteria, as a consequence of the protease activity, become coated with incompetent Fab. fragments instead of with intact antibody molecules. Using a combination of nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting, we detected Fab. fragments not only on oral streptococci (Streptococcus sanguis and Streptococcus gordonii) incubated in saliva but also on the bacteria in incipient dental plaque. These results are of relevance to our previous observation that IgAl protease activity may neutralize the ability of S-IgA antibodies to inhibit the adherence of oral streptococci to saliva-coated hydroxyapatite.