[Immune effects research of interleukin 12 and Mycobacterium tuberculosis ESAT-6 antigen combined DNA immunization].

To investigate the immune effects of combined DNA immunization of human interleukin 12 and Mycobacterium tuberculosis ESAT-6 antigen. Thirty BALB/c mice were divided into 5 groups. They were immunized inter-muscularly with 100 microL solution of normal saline (group A), pcDNA3.1 control plasmid (group B), pcESAT-6 plasmid (group D) and pcIL-12 + pcESAT-6 plasmid (group E), respectively, for three times with 2 weeks interval. At the last time immunization, group C mice were immunized intra-dermally with 10(6) CFU BCG suspended in normal saline in a volume of 100 microL. After the last immunization 14 and 28 days, groups of mice (three mice per group) were sacrificed and separated their serum and splenocytes at once, respectively. The sera were cryopreserved for antigen-specific antibody production tests with ELISA. The separated mice spleen cells were cultured with completed RPMI 1640 medium in vitro. Specific splenocytes proliferation responses to TB-PPD antigen were measured by XTT colorimetry after five days culture. Another part of the culture spleen cells were stimulated with TB-PPD antigen for three days, then collected the supernatants to determine IFN-y and IL-4 secretions level by ELISA test as well, respectively. The results show that both ESAT-6 immunization and IL-12 + ESAT-6 combined immunization induce significantly anti-TB-PPD antibody production. Further, the antigen-specific splenocytes proliferation and IFN-gamma production level of IL-12 + ESAT-6 combined immunization are higher than pcESAT-6 or BCG immunization alone (P < 0.05). However, it displays no distinct differences of IL-4 secretion among ESAT-6, BCG and IL-12 + ESAT-6 combined immunization groups. It indicates that ESAT-6 immunization combined with IL-12 could induce much stronger specific cellular immunity than only ESAT-6 or conventional BCG immunization. (Therefore, codelivery of an IL-12 secreting plasmid with M. tuberculosis antigen may be a potent strategy for enhancing cellular immunity against M. tuberculosis.