Species-specific monoclonal antibodies to Rickettsia japonica, a newly identified spotted fever group rickettsia

A total of 192 hybridomas were developed from mice immunized with Rickettsia japonica, a newly identified spotted fever group rickettsia pathogenic for humans. Of these hybridomas, 101 were species specific, 37 were spotted fever group reactive, and the other 54 were also reactive with one or more of the other pathogenic species of spotted fever group rickettsiae, Rickettsia akari, Rickettsia australis, Rickettsia conorii, Rickettsia rickettsii, and Rickettsia sibirica. Seven of the species-specific monoclonal antibodies were characterized. These monoclonal antibodies all belong to the immunoglobulin G class and react with all five strains of R. japonica at the immunofluorescence titers, indicating that the five strains all belong to a single species. The species-specific epitopes reactive with these monoclonal antibodies are located on the surface proteins of the organisms demonstrated as 145- and 120-kilodalton bands on Western immunoblots. These two antigenic bands were shown to be proteins, because treatment with proteinase K completely destroyed the reactivity of the bands with the monoclonal antibodies.