01). Ub fusion DNA vaccine enhanced the cytotoxic T cell response,
compared with Ag85A DNA inoculation (P < 0.05). The blank vector or pcDNA3-ub immunization did not induce CTL response. The spontaneous release was below 10%. It has been reported that DNA vaccines preferentially induced Th1-dominant immune response. The exact mechanism of driving Th1- or Th2-type response has not been well known, but it has been suggested that CpG motifs from a bacterial plasmid might be responsible for driving immune responses towards Th1 type. Th1-type response has been reported to correlate with protective immunity in certain tumour, bacterial or viral infection, as well as some parasitic disease. Protective immunity against tuberculosis mainly depends
Crizotinib on cellular immune responses and some cytokines of Th1 type, such as IFN-γ. Hence, to improve the DNA vaccines against Mycobacterium see more tuberculosis, some strategies must be explored to enhance the protective immune response. In our study, we chose ub to modulate the immune response elicited by Ag85A DNA vaccine. It is well known that ub–proteasome pathway is the main source for intracellular protein turnover. MHC class I most often presents peptides derived from endogenously synthesized proteins, which are degraded by the proteasome. Hence, higher rates of intracellular antigen turnover should increase the number and variety of fragments and peptides available for MHC I binding, which may result in an increase in cell-mediated response to the expressed antigens. To this point, conjugation of the antigen with ub should target the endogenously synthesized antigens to the proteasome pathway and result in an enhanced cellular immune response. Some researchers have optimized the efficacy of DNA vaccines by increasing the antigen degradation [22–25]. There are two methods of fusing the ub with the interest protein. One is to mutate the C-terminal residue of Ub from glycine Erastin in vitro (G) to alanine (A), resulting in a stable ub-protein (UbAAg). This stable ub-protein can be polyubiquitinated and degraded quickly by the proteasome. The other method
is to add an arginine (R) to the C-terminus of ub, resulting in an unstable ub-protein (UbGR-Ag). This fusion protein can be quickly recognized and degraded by the ub system according to the N-end rule, also resulting in promoted protein degradation. Based on the ub paradigm, we fused UbGR with Ag85A antigen from M.TB in our study. The change in the immune response elicited by UbGR-Ag85A fusion DNA vaccine indirectly showed the change in Ag85A degradation. Compared with the Ag85A DNA immunization, UbGR-Ag85A fusion DNA vaccine resulted in an lower antibody IgG, an enhanced lymphocytes proliferation, a stronger Th1-type immune response and an enhanced cytotoxicity of CTL. To generate a protective immune response against infection by Mtb, CD4+ and also CD8+ T cell responses are essential.