Proteic boost enhances humoral response induced by DNA vaccination with the dnaK gene of Chlamydophila abortus but fails to protect pregnant mice against a virulence challenge

In order to enhance the quantity and the protective properties of the antibodies induced by DNA vaccination with the heat shock protein dnaK gene of Chlamydophila abortus AB7 as well as to elicit an efficient cellular immune response, we vaccinated mice with a DNA prime followed by a boost with the recombinant DnaK protein. In non-pregnant mice, this strategy induced the same predominance of the IgG2a isotype as DNA immunization alone with a substantial increased antibody level. The induced antibodies had no in vitro neutralizing properties on C. abortus infectivity. Moreover, the proteic boost probably failed to elicit an efficient cellular immune response since the pregnant or non-pregnant mice were not protected against the bacterial challenge.