Cell-mediated immune responses and protective efficacy against infection with Mycobacterium tuberculosis induced by Hsp65 and hIL-2 fusion protein in mice.

Heat shock protein 65 (Hsp65) is an important immunodominant antigen against tuberculosis (TB), and interleukin-2 (IL-2) plays an important role in the regulation of antimycobacteria immune responses. In order to further increase the immunogenicity of Hsp65 against infection caused by Mycobacterium tuberculosis (MTB), we expressed MTB Hsp65 and human IL-2 fusion protein, Hsp65-hIL-2, in Escherichia coli. The expression of Hsp65-hIL-2 was confirmed by Western blotting using anti-Hsp65 MoAb and anti-hIL-2 MoAb, respectively. Hsp65-IL-2 and Hsp65 were then purified by Ni-NTA affinity chromatography. Mice were immunized with purified Hsp65-hIL-2 or Hsp65 emulsified in the adjuvant combination dimethyl dioctadecylammonium bromide and monophosphoryl lipid A. Eight weeks after immunization, there was significant proliferation of spleen lymphocytes in response to both Hsp65 and Hsp65-hIL-2 proteins. Interestingly, Hsp65-hIL-2 fusion protein elicited significantly higher levels of IFN-gamma and IL-2 in the lymphocytes culture supernatant than that of the BCG (Denmark strain) immunized group and Hsp65 group (P < 0.05). After challenging the immunized mice with MTB, the bacteria loads in the spleens and lungs of mice immunized with the fusion protein were significantly lower than Hsp65 alone group, reaching an equivalent level as BCG immunization group. Our results suggest that the Hsp65 and hIL-2 fusion protein may serve as an alternative vaccine candidate against MTB infection.