Defense Date


Document Type


Degree Name

Doctor of Philosophy


Microbiology & Immunology

First Advisor

John G. Tew


This study was initiated to look for characteristics of the immunodominant antigen(s) of Actinobacillus actinomycetemcomitans (Aa) that might help explain the high antibody titers reactive with this organism in periodontitis patients. Radioimmunoassays (RIA) and limiting dilution analysis on western blots were used to identify and characterize the immunodominant antigens of Aa in high responder patients (i.e. patients with high antibody titers). Additional experiments focused on specific responding subjects with a range of antibody titers to serotype b (AaY4). This group included both white and black subjects. Similar studies then examined the immunodominant antigens of Aa serotypes a and c. The Aa serotype specificity of the high responders was determined and further work was confined to individuals responding specifically to serotypes a or c. The results indicated that the immunodominant antigen of Aa Y 4 in all high responders was heat and papain stable. Limiting dilution analysis on western blots showed that a large diffuse band resembling carbohydrate was the immunodominant antigen. Partially purified AaY4 carbohydrate also contained the large diffuse band. Double immunodiffusion (Ouchterlony) tests indicated that the dominant antigen recognized in the carbohydrate extract by the patients' sera was the same antigen recognized by serotype b specific rabbit antiserum which has been previously shown to react with the serotype specific carbohydrate of AaY4. When the subjects with specific antibody responses covering a range of positive antibody titers were examined, 95% of the subjects were responding to the smeared serotype specific carbohydrate antigen on western blots. For serotype-a, no immunodominant antigen was common to the majority of high responding subjects. For serotype-c two antigens were immunodominant in the majority of the high responding patients: 92% had an antigen with a diffuse smeared appearance on western blots typical of a carbohydrate antigen and 67% had an approximately 15Kd antigen. The smeared antigen gave a reaction of identity with patient serum and serotype c specific rabbit antiserum in double immunodiffusion assays. These findings indicated that the immunodominant antigen for serotypes-b and-c in high responding subjects was the serotype specific carbohydrate. The same antigen was immunodominant for subjects with a range of antibody titers to AaY4. The dominant antigen was highly variable for serotype-a. These antigens were highly immunogenic. This immunogenicity may explain the enormous antibody titers observed for Aa in response to what appears to be a small quantity of antigen.


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