[Plasmid encoding human IL-12 improve protective efficacy of Mtb8.4 gene vaccine with signal sequence against infection of Mycobacterium Tuberculosis].

AIM

To study the specific celluar immune response and protective efficacy induced by co-immunization of DNA vaccine of Mtb8.4 with signal sequence (MS) and plasmid encoding human interleukin 12 (hIL-12).

METHODS

Fourty C57BL/6N mice were randomly divided into the following groups: MS gene vaccine plus plasmid of hIL-12, MS gene vaccine, BCG, vacant vector alone and PBS. Mice were immunized intramuscularly in both hind limbs three times at the intervals of three weeks or once subcutaneously with 1 x 10(6) of viable M.bovis BCG Pasteur at the time of the first DNA immunization (BCG group). Four weeks after the final inoculation, three mice per group were sacrificed to assess cytokine response by ELISA methods and CTL activities with LDH release assay. The other five mice per group were challenged intravenously in a lateral tail vein with 1 x 10(6) CFU of virulent M.Tuberculosis H37Rv. Spleen and the left lung were harvested from each mouse at 4 weeks after infection and homogenized in sterile. Serial dilutions of organ homogenates were plated on L-J agar and incubated 37 degrees Celsius until colonies were visible 4 weeks later. Protective efficacies in each experiment were expressed as reduced CFU and were compared with that in the negative control group. The right lung was obtained from each mouse and inflated with and stored in 10% formalin immediately. Tissues were embedded in paraffin, sectioned and stained with hematoxylin and eosin.

RESULTS

Co-immunization with MS gene vaccine and plasmid encoding hIL-12 induced the secretion of more of Th1 cytokines, but not IL-4, and enhanced CTL activity; while BCG induced the secretion of both types of cytokines (IFN-gamma, IL-2 and IL-4). Co-immunization with MS gene vaccine and plasmid encoding hIL-12 could remarkably reduced CFU counts in organs.

CONCLUSION

Plasmid encoding hIL-12 can improve the specific cellular immune response and protective efficacy induced by the MS gene vaccine alone.