DNA immunization confers systemic, but not mucosal, protection against enteroinvasive bacteria

Naked plasmid DNA (pRc/Y-hsp60) with a cytomegalovirus promoter and a seque nce encoding Yersinia enterocolitica 60-kDa heat shock protein (Y-HSP60) wa s used for vaccination. After intramuscular injection of pRc/Y-hsp60, Y-hsp 60 mRNA could be detected by reverse transcription-PCR in muscle, liver and spleen. A single immunization with pRc/Y-hsp60 induced significant Y-HSP60 -specific T cell responses after 1 week. IFN-gamma production by spleen cel ls upon stimulation with Y-HSP60 was strictly dependent on the presence of CD4(+) T cells, indicating the generation of a Th1 response upon DNA immuni zation. DNA immunization in addition induced strong Y-HSP60-specific IgG2a, weak IgG1, but not IgA antibodies. Immunization of BALB/c and C57BL/6 mice with pRcr/-hsp60 conferred protection against disseminated Y. enterocoliti ca infection in spleen, but not at the site of mucosal entry, the Peyer's p atches. Furthermore, pRc/Y-hsp60 vaccination did not induce cross-protectio n against related pathogens. Vaccination of beta(2)-microglobulin- and H2-I -A beta-deficient mice was not protective, suggesting that both CD4(+) and CD8(+) T cells are required for protective immunity induced by DNA vaccinat ion.