PROLIFERATION OF DISTINCT HUMAN T-CELL SUBSETS IN RESPONSE TO LIVE, KILLED OR SOLUBLE EXTRACTS OF MYCOBACTERIUM-TUBERCULOSIS AND MYCO-AVIUM

The proliferative responses of distinct cell subsets from healthy, bac ille Calmette-Guerin (BCG)-vaccinated blood donors were assessed after ill vitro stimulation with live or UV-killed Mycobacterium tuberculos is and Myco. avium or with soluble extracts obtained from either mycob acterial species. Proliferation of cell subsets was evaluated by flow cytometric determination of 5-bromo-2'-deoxy-uridine incorporation int o DNA and simultaneous identification of surface phenotypic markers. I n the presence of monocytes, the response to whole (live or killed) ba cteria was characterized by a predominant proliferation of CD4(+) alph a beta(+) T cells and, to a lesser extent, of CD8(+) alpha beta(+) T c ells. Proliferation of CD8(+) alpha beta(+) T cells was primarily elic ited by live rather than killed bacilli (P < 0.05). Conversely, when s oluble bacterial extracts were used as stimulators, a preferential pro liferation of gamma delta(+) T cells, expressing predominantly V gamma 9(+) and V delta 2(+) T cell receptor chains, was recorded. Moreover, when monocyte-depleted cell populations were directly cultured with l ive bacteria, a marked proportion of CD3(-)CD16(+) (natural killer (NK )) cells was detected among the responding cells. Although both alpha beta, gamma delta and NK cells have been previously shown to react wit h mycobacteria in vitro, their relative contributions to the response have been difficult to assess. Using a flow cytometric technique which allows direct identification of proliferating cells within complex ce ll populations, our study demonstrates significant differences in the ability of various mycobacterial antigen preparations to elicit prolif eration of distinct cell subsets.