Immunodominant antigens of Actinobacillus actinomycetemcomitans serotype b in early‐onset periodontitis patients

Previous work with Actinobacillus actinomycetemcomitans strain Y4 (serotype b) indicates that the immunodominant antigen in high‐responding patients (top 10%, 80% of which were black) is the serotype‐specific antigen. In this study we examined the immunodominant antigens of A. actinomycetemcomitans strain Y4 in both black and white patients having a range of antibody titers. We sought to test the hypothesis that the immunodominant antigen in these subjects was the same antigen found in high responders. Seropositive white early‐onset periodontitis (EOP) patients were selected from 99 EOP patients. Black subjects were then selected with comparable antibody titers. Double immunodiffusion and competition assays were used to determine whether reactive antibodies were A. actinomycetemcomitans serotype b‐specific or whether the response was to serotype a or c. The immunodominant antigens were then determined for the patients reacting specifically to A. actinomycetemcomitans Y4 using limiting dilution analysis on Western blots. The immunodominant antigen for the A. actinomycetemcomitans Y4‐specific patients appeared to be the serotype‐specific carbohydrate for most subjects (19/20 or 95%, including: 13/14 black and 6/6 white patients). In conclusion, the immunodominant antigen for A. actinomycetemcomitans Y4 was the serotype‐specific carbohydrate regardless of antibody titer for both black and while specifically reactive patients.