Immunization with a portion of rickettsial outer membrane protein A stimulates protective immunity against spotted fever rickettsiosis.

Two approaches for presentation of a part of the rickettsial outer membrane protein A (OmpA) of Rickettsia rickettsii, namely (1) recombinant Mycobacterium vaccae (rMV) or (2) recombinant DNA vaccine, stimulated protective immunity against a lethal challenge with the closely related bacterium, R. conorii, in mice. After primary immunization with rMV and booster immunization with homologous recombinant protein, 67 and 55% of mice were protected against challenge in two experiments. DNA vaccination with booster recombinant protein immunization protected six out of eight animals from a lethal challenge. Production of IFN-gamma by antigen-exposed T-lymphocytes of DNA vaccine recipients indicated that cellular immunity had been stimulated.