Immunoreactivity in humans of Bacteroides gingivalis hemagglutinating adhesin HA-Ag2

A rabbit antiserum monospecific for HA-Ag2, a hemagglutinating adhesin of Bacteroides gingivalis, was used as a reference to screen sera from 8 patients with chronic periodontitis and 6 normal subjects for specific antibodies. The monospecific antiserum detected a complex of 2 polypeptides with molecular weights of 43 and 49 kDa in an outer membrane preparation of B. gingivalis. All human sera reacted with one or both polypeptides in at least one of the isotypes (IgG, IgA and IgM) tested, indicating that HA-Ag2 is an immunodominant antigen. Although the 2 components of HA-Ag2 are antigenically similar, a trend toward preferential reactivity of IgM with the 49 kDa component was observed. This suggests that an epitope-specific mechanism of regulation of the immune response to B. gingivalis in humans may exist via the HA-Ag2 complex.