Immunological Function Of Fragment PGRS Of Rv1818c Of PE Protein Family In Mycobacterium Tuberculosis

Tuberculosis is a major cause of death worldwide and is the commonest cause of death due to a single infectious agent. Mycobacterium tuberculosis, the causative of tuberculosis, is a successful intracellular pathogen and can live within macrophage, a significant cell of host immune system whose function is the elimination of microbes.Host infected with Mycobacterium tuberculosis mount a strong immune response to control the Mycobacterium tuberculosis infection, eliciting CD4~+ , CD8~+ T cells as well as antibodies specific for mycobacterial antigens. But , Mycobacterium tuberculosis persists within macrophage through a variety of immune evasion strategies, including preventing the recognition of infected macrophage by T cells and evading macrophage killing mechanisms, which result in latent infection. However , in some circumstances the host immune response is perturbed and reactivation of latent infection results. This process canoccur, for example, through HIV infection, the use of immunosuppressive medication or advanced age. Surveys with purified protein derivative(PPD) or tuberculin skin test suggeste that one-third of the world's population is infected with Mycobacterium tuberculosis. Primary infection leads to active disease in only a minority (about 10%) of infected individuals. In the remaining 90% of cases the immune system contains the infection, and the individual is non-infectious and symptom-free. The large amount of latent infected individual is the major source of reactivation, so control the latent infection is critical for preventing the spread of tuberculosis throughout the world.In this study, we constructed a eukaryotic expression plasmid pcDNA-EP in which a fusion gene of ESAT-6 coding sequence and PGRS fragment of Rvl818c was cloned. Subsequently, the recombinant eukaryotic expression plasmid was used to transfect cultured Balb/c3T3 cell by using cationic liposomes. The expression products were determined by using RT-PCR. Then, the plasmid was injected intramuscularly for C57BL/6J mice on days 1, 14, 28. Immunogenicity of pcDNA-EP were detected 21 days after the last immunization. T lymphocytes obtained from the spleen of pcDNA-EP immunized mice exhibited higher lymphocyte proliferative response and IFN- y production than that of control plasmid immunized mice. The metabolism inhibition experiment showed that the higher lymphocyte proliferative response and IFN- Y production was restricted by MHC class II molecular. The results indicated that itwas the CD4+ T cells but not the CD8+ T cells which response to the immunogenicity of the recombinant eukaryotic plasmid pcDNA-EP.