Proliferative response and antibody production against SA5K, a secretion protein of M. tuberculosis in healthy subjects and patients with tuberculosis

Over the last few years proteins actively secreted in culture filtrates by Mycobacterium tuberculosis have been the object of extensive studies as they are considered immunodominant antigens able to induce a protective immunity in animal models. A new 8.3 kDa secretion protein released in culture filtrates by M. tuberculosis, M. bovis BCG, and a few other mycobacterial species has recently been described in our laboratory. The aim of the present study was to purify the protein from recombinant E. coli cells and to test its immunological potential in healthy subjects and tuberculous patients. The results obtained demonstrated that SA5K is able to induce in vitro proliferation of CD4 + T lymphocytes from healthy M. bovis BCG-vaccinated subjects, but not from patients with tuberculosis. The poor specificity displayed by the recombinant antigen when tested in Western blotting with sera obtained from healthy subjects and tuberculous patients, does not suggest, at least in the recombinant form, its employment for a serodiagnosis of tuberculosis.