The nature of immunodominant antigens of periodontopathic bacteria

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The present study had the purpose 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, sonicated extract and outer membrane protein of P. gingivalis 381 were used as antigen in untreated and heated form. Total sugar, protein and lipopolysaccharide were estimated in each one of the three antigens. Antibody binding to the three antigens was evaluated, before and after heat treatment, by an enzyme-linked immunosorbent assay (ELISA). In addition, the immunoblotting analysis was performed. The quantitative assays showed that the whole cell contained about ten times more lipopolysaccharide while the outer membrane protein contained twice the amount of carbohydrates. The 14 sera were classified into three groups according to the rate of reduction of antibody binding under heat treatment. Concerning the sonicated extract, the antibody binding showed high reduction (77.5-92.3%) under heat treatment in 11 out of 14 sera. However, antibody binding to the outer membrane protein antigen was hardly decreased by heat treatment in three sera (14.9-30.9%). Also, these three sera showed almost the same response to the whole cell antigen (reduction 15.2-24.9%). The present study indicates that the immunodominant antigens of P. gingivalis seemed to be composed mainly of protein and appeared to be at molecular weights of 57, 44, 42 and 39 kDa. Furthermore, a possibility that non-proteinic substances, may contribute to the antibody binding as an antigen is indicated from the results of the whole cell and the outer membrane protein.