Bacteroides melaninogenicus has been shown to play an essential role in certain mixed anaerobic infections. It has further been ascribed a role as a dominant pathogen in certain types of periodontal disease and has been shown to induce rapidly advancing periodontal disease when introduced in a pure inoculum into germ-free rats. We propose to study the cell surface antigens of B. melaninogenicus. We have successfully isolated, purified, and partially characterized the major antigens using gel chromatography and various immunochemical techniques. Using purified antigens we have begun to study the humoral immune response in animals infected by B. melaninogenicus, by means of a sensitive radioactive antigen binding assay. Specific studies will be conducted utilizing a germ-free rat model, where organisms can be introduced in a controlled fashion, thereby facilitating the interpretation of immunologic data. Serologic tests will be developed, using purified antigens for potential use in defining serogroups within this species, and as rapid diagnostic methods for determining the presence of B. melaninogenicus in clinical infection. Ultimately, we propose to study the potential for use of these purified antigens as vaccines for the protection against oral infections by B. melaninogenicus, specifically periodontal disease.