IL-10 down-regulates the expression of survival associated gene hspX of Mycobacterium tuberculosis in murine macrophage

Abstract Mycobacterium tuberculosis (MTB) adopts a special survival strategy to overcome the killing mechanism(s) of host immune system. Amongst the many known factors, small heat shock protein 16.3 (sHSP16.3) of MTB encoded by gene hspX has been reported to be critical for the survival of MTB. In the present study, the effect of recombinant murine interferon-gamma (rmIFN-γ) and recombinant murine interleukin-10 (rmIL-10) on the expression of gene hspX of MTB in murine macrophage RAW264.7 has been investigated. By real-time RT-PCR, it was observed that three increasing concentrations (5, 25 and 50 ng/ml) of rmIFN-γ significantly up-regulated the expression of hspX whereas similar concentrations of rmIL-10 (5, 25 and 50 ng/ml) significantly down-regulated the hspX expression. This effect was not only dependent on the concentration of the stimulus but this was time-dependent as well. A contrasting pattern of hspX expression was observed against combinations of two different concentrations of rmIFN-γ and rmIL-10. The study results suggest that rIL-10 mediated down-regulation of hspX expression, in the presence of low concentration of rIFN-γ, could be used as an important strategy to decrease the dormancy of MTB in its host and thus making MTB susceptible to the standard anti-mycobacterial therapy used for treating tuberculosis. However, as these are only preliminary results in the murine cell line model, this hypothesis needs to be first validated in human cell lines and subsequently in animal models mimicking the latent infection using clinical isolates of MTB before considering the development of modified regimens for humans.

Analysis of immunogenicity of tuberculosis fusion protein consisting of Ag85B, Mpt64 and HspX antigens expressed in replication and dormancy bacilli / 中华微生物学和免疫学杂志

Objective To construct protective immunity to Mycobncterium tuberculosis latent infection, a novel fusion protein consisting of HspX, the 190 to 198 peptide of Mpt64 and Ag85B, which were confirmed to be the effective protective antigens mainly expressed in the dormancy and exponential phase of growth, was constructed and its immunogenicity was investigated. Methods Ag85B and Mpt64190-198-HspX sequences were amplified by PCR and cloned into plasmids pET-28a. The fusion protein, Ag85BMpt64190-198-HspX (AMH) was expressed in E. coli BL21 and purified with Ni-NTA resins. C57BL/6 mice were immunized three times at 2-week intervals subcutaneously with AMH formulated with the adjuvant composed of dimethyl-dioctyldecyl ammonium bromide (DDA) and BCG polysaccharide nucleic acid (BCGPSN). Humoral and cell-mediated immunity responses were analyzed at five weeks after the last injection. Results AMH was expressed stably in E. coli and could be purified well by Ni-NTA affinity chromatography. C57BL/6 mice immunized with AMH subunit vaccine generated specific cellular and humoral immunologic response to the stimulation of Ag85B, Mpt64190-198 and HspX. Conclusion It suggested that AMH was a promising candidate antigen of tuberculosis subunit vaccine.