Analysis of immunodominant antigens of Porphyromonas gingivalis 381 in high responder patients.

The purpose of this study was to determine the immunodominant antigens of P. gingivalis 381 and to examine their composition and molecular weight. Fourteen periodontal patients, with high antibody titers to P. gingivalis 381 sonicated extract, were selected. Whole cell fraction, sonicated extract and outer membrane protein of P. gingivalis 381 were used as antigens in the untreated form as well as in the heated form and treated with papain. Total volume of sugar, protein and lipopolysaccharide (LPS) was estimated in each one of the three antigens. Antibody binding capacity to the three antigens was evaluated, before and after heat and papain treatment, by an enzyme-linked immunosorbent assay (ELISA). In addition, the immunoblotting analysis was performed. The quantitative assays showed that the whole cell fraction contained about ten times more LPS than the other two preparations while the outer membrane protein contained twice the amount of carbohydrates than the other two preparations. The 14 sera were classified into three groups according to the rate of reduction of antibody binding under heat and papain treatment. Concerning heat treatment, most of the sera showed a high reduction of antibody binding when reacting with the sonicated extract. However, antibody binding to the outer membrane protein antigen was hardly decreased by heat treatment in three sera. Also, these three sera showed almost the same response to the whole cell fraction antigen under heat treatment. Under papain treatment, almost all sera showed a moderate reduction of antibody binding when they reacted with the sonicated extract and whole cell fraction while they showed a low reduction of antibody binding when they reacted with the outer membrane protein. From the present study it could be concluded that a main proteinaceous antigen of P. gingivalis was recognized by the majority of the patients suggesting that the proteinaceous portion is an important part of the antigen, while some patients seemed to recognize the LPS or carbohydrate as the antigenic determinant.