Protection of guinea-pigs from experimental Rocky Mountain spotted fever by immunization with baculovirus-expressed Rickettsia rickettsii rOmpA protein.

Baculovirus recombinants that express the Rickettsia rickettsii rOmpA protein were constructed. Monoclonal antibodies (mAbs) against the rOmpA protein reacted with recombinant-infected Spodoptera frugiperda (Sf9) cells in indirect immunofluorescence assays. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting of infected Sf9 cell lysates with a mAb against rOmpA showed that the recombinant-expressed rOmpA protein migrated slightly below rOmpA extracted from R. rickettsii. Guinea-pigs immunized with lysates of recombinant-infected Sf9 cells developed antibodies reactive with R. rickettsii and were protected against challenge, indicating that the baculovirus-expressed rOmpA protein could be useful in subunit vaccines and for studies of the immune response to R. rickettsii infection.