IMMUNOGLOBULIN CLASS AND SUBCLASS DISTRIBUTION OF ANTIBODIES REACTIVEWITH THE IMMUNODOMINANT ANTIGEN OF ACTINOBACILLUS-ACTINOMYCETEMCOMITANS SEROTYPE-B

The aims of this study were to determine the immunodominant antigens o f Actinobacillus actinomycetemcomitans serotype b (Aab) for the differ ent immunoglobulin (Ig) classes and subclasses and to determine the re lative levels of these different Igs in serum. Seropositive early-onse t periodontitis patients were sampled, and the Ig classes IgG, IgA, an d IgM and subclasses IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2 were studi ed. Reactivity with Aab antigens was assessed by using the Western blo t (immunoblot) in limiting dilution analysis and radioimmunoassay with sera from 13 early-onset periodontitis subjects. A smeared antigen in the upper portion of the immunoblots, typical of high-molecular-weigh t LPS, was immunodominant for IgG, IgA, IgM, IgG1, IgG2, IgG3, IgA1, a nd IgA2. This smeared antigen was present in every patient for all of these Igs at the endpoint. A few additional antigens were also present at the endpoint in some patients, but none were present in more than half of the subjects. The distribution of antibody titers by Ig classe s reactive with the Aab immunodominant antigen was IgG > IgA > IgM. Th e distribution of antibody titers by IgG subclass was IgG2 > IgG1 almo st-equal-to IgG3. Further quantitation by radioimmunoassay revealed th at the mean concentration of IgG2 (65.7 mug/ml) was significantly grea ter than that of IgG1 (8.8 mug/ml). The IgA subclass distribution was IgA1 >> IgA2, with IgA1 apparently being second only to IgG2. Therefor e, the Aab antigen eliciting the highest antibody level in virtually a ll Ig classes and subclasses appeared to be lipopolysaccharide, and Ig G2 was markedly elevated over all other serum Ig classes or subclasses reactive with Aab.