A DNA vaccine protects mice against the rickettsial agent Cowdria ruminantium

A DNA vaccine (VCL1010/MAP1) containing the major antigenic protein 1 (MAP1 ) gene of Cowdria ruminantium, driven by the human cytomegalovirus (HCMV) e nhancer-promoter, was injected intramuscularly into 8-10 week-old female DB A/2 mice after treating them with 50 mu l/muscle of 0.5% bupivacaine three days previously. Up to 75% of the immunized mice seroconverted and reacted with C. ruminantium antigen blots. Splenocytes from immunized mice, but not from control mice, proliferated in response to the recombinant MAP1 and to C. ruminantium antigens in in vitro lymphocyte proliferation tests. These proliferating cells secreted IFN-gamma and IL-2 at concentrations ranging f rom 610 pg/ml to 1290 pg/ml and from 152 pg/ml to 310 pg/ml, respectively. Only up to 45 pg/ml and 42 pg/ml of IFN-gamma and IL-2, respectively were d etected in supernatants of splenocytes from control mice. In experiments re sting different VCL1010/MAP1 DNA vaccine dose regimens (25-100 mu g/dose, t wo or four immunizations), survival rates of 23% to 88% (35/92 survivors/to tal in all VCL1010/MAP1 immunized groups) were observed on challenge with a lethal dose of cell culture-derived C. ruminantium organisms. In contrast, survival rates of 0% to 3% (1/144 survivors/total in all control groups) w ere recorded for control mice. This study demonstrates that MAP1 is a prote ctive antigen and validates the concept of DNA vaccines against heartwater.