Immunoprophylactic properties of 71-kDa cell wall-associated protein antigen of Mycobacterium tuberculosis H₃₇Ra

Abstract

Proteins associated with the cell wall peptidoglycan (CW-Pr) of Mycobacterium tuberculosis H₃₇Ra were isolated to evaluate their immunoreactivity and immunoprophylactic properties against experimental tuberculosis. Chemical treatment of the cell wall with trifluoromethanesulfonic acid: anisole (2 : 1) resulted in the release of three proteins of 71, 60 and 45 kDa as resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A comparative study of immune responses elicited to individual proteins in mice immunized with CW-Pr emulsified in incomplete Freund's adjuvant showed the 71-kDa protein to be the most immunoreactive antigen. This 71-kDa protein was found to cross-react with the 70-kDa heat shock protein from M. leprae and possessed ATPase activity. Mice immunized with the 71-kDa protein exhibited significantly higher immune responses, on the basis of T and B cell reactivity, as compared to a M. bovis Bacillus Calmette Guerin (BCG)-vaccinated group. The culture supernatants collected from 71-kDa stimulated lymphocytes stimulated exhibited increased interferon-γ and interleukin-2 production. The protective efficacy of the 71-kDa protein in comparison to BCG was determined by challenging the mice with a virulent strain M. tuberculosis H₃₇Rv. The 71-kDa protein was found to be more protective in animals challenged at 8 and 16 weeks post immunization, shown by increased survival rates and decreased viable bacilli counts in the target organs as compared to BCG-vaccinated animals.