IMMUNOBIOLOGICAL PROPERTIES OF A 30-KDA SECRETORY PROTEIN OF MYCOBACTERIUM-TUBERCULOSIS-H37RA

Six different secretory proteins of molecular weights (15, 26, 30, 41, 55 and 70 kDa) were isolated from 8-day-old culture filtrate of Mycob acterium tuberculosis H37Ra using different column chromatography tech niques. These proteins were further examined for their ability to indu ce cell mediated (T-cell proliferation assay) and humoral immune respo nse (ELISA) in mice immunized with total culture filtrate proteins. Ou t of six proteins, three proteins showed good reactivity. However, the activity was at a maximum with 30 kDa antigen. The immune response in duced by 30 kDa antigen emulsified in Freund's incomplete adjuvant (FI A) was investigated and was found to be dose dependent. The T-cell res ponse induced by this protein was skewed rewards T-helper (Th1) cells as determined by the pronounced secretion of interleukin-2 (IL-2) and gamma-interferon (IFN-gamma). The protective activity of the 30 kDa pr otein was also evaluated and compared with reference to Bacillus Calme tte Guerin (BCG) vaccine in the mice challenged with virulent M. tuber culosis H(37)Rv. The degree of protection afforded by the 30 kDa antig en on the basis of mortality and the significant decrease in c.f.u.'s recovered from different organs (lung, liver, spleen) after 30 days of challenge with LD50 of M. tuberculosis H(37)Rv was significantly high er in comparison to BCG vaccinated animals. However, the degree of imm unity induced by this antigen decreased with time (when challenged 8 a nd 12 weeks post-immunization) but it was still comparable with BCG, T hese findings suggest that 30 kDa secretory protein of M. tuberculosis is the key immunoprotective antigen and may be a suitable candidate f or the development of an alternative subunit vaccine against tuberculo sis. (C) 1997 Elsevier Science Ltd.