Identification of strain-specific and group-reactive antigenic determinants on the Karp, Gilliam and Kato strains of Rickettsia tsutsugamushi

Hybridoma antibodies (Hab) were prepared against the Karp, Gilliam and Kato strains of Rickettsia tsutsugamushi and were examined for homologous and heterologous reactivity using an indirect immunofluorescence assay. Strain-specific Hab demonstrated homologous IFA titers ranging from 1/320 to 1/1,280 and did not react (less than 1/10) with the heterologous strains. The cross-reactive Hab generally reacted equally with all three strains in the scrub typhus group; however, there were some Hab that reacted with only one of the two heterologous strains tested. The Hab also were examined in enzyme-linked immunosorbent assays with scrub typhus antigens eluted from SDS-polyacrylamide gels. Most Hab reacted with either one or several of the six eluted antigens detected with a polyclonal immune serum. It was also observed that strain-specific and cross-reactive Hab sometimes reacted with the same antigen, suggesting the existence of multiple antigenic determinants in one electrophoretic peak. The data suggest that strain-specific Hab can be used in the indirect immunofluorescence assay to identify isolates of R. tsutsugamushi without the cross-reactions usually observed with polyclonal antisera, and that they are useful probes for detection and analysis of rickettsial antigens.