Protection against scrub typhus by a plasmid vaccine encoding the 56-KD outer membrane protein antigen gene.
The 56-kD outer membrane protein of Orientia tsutsugamushi has previously been shown to be the immunodominant antigen in scrub typhus infections. Its gene was cloned into the DNA vaccine vector pVR1012 as a vaccine candidate (pKarp56). The in vitro expression of this 56-kD antigen by pKarp56 was confirmed in tissue culture by an indirect fluorescence assay and Western blot analysis. The initial antibody responses of mice immunized with varied doses of the pKarp56 were barely detected, but increases were observed after each of three subsequent booster immunizations. Although no protection was observed with a single immunization of pKarp56, after four immunizations, 60% of the mice survived a 1,000 x 50% lethal dose (LD(50)) challenge. These results specifically confirm the importance of the 56-kD protein antigen in protective immunity against O. tsutsugamushi and demonstrate the feasibility of DNA vaccines for the prevention of scrub typhus.
Ni
Yi-Sheng
YS
Rickettsial Diseases Department, U.S. Naval Medical Research Center, Silver Spring, Maryland 20910, USA.
Chan
Teik-Chye
TC
Chao
Chien-Chung
CC
Richards
Allen L
AL
Dasch
Gregory A
GA
Ching
Wei-Mei
WM
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000276:immunology*; D001428:Bacterial Vaccines / Q000235:genetics / Q000276:immunology*; D002460:Cell Line; D005260:Female; D006801:Humans; D007114:Immunization; D051379:Mice; D012285:Orientia tsutsugamushi / Q000276:immunology* / Q000472:pathogenicity; D010957:Plasmids / Q000235:genetics*; D012612:Scrub Typhus / Q000276:immunology / Q000401:mortality / Q000517:prevention & control*; D019444:Vaccines, DNA / Q000276:immunology
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001428:Bacterial Vaccines; D019444:Vaccines, DNA