Identification of distinct lymphocyte subsets responding to subcellular fractions of Mycobacterium bovis bacille Calmette-Guerin (BCG)

In order to investigate the ability of Mycobacterium bovis BCG vaccination to induce immune responses toward different classes of mycobacterial antige ns and the cell populations involved in such responses, proliferation of di stinct human lymphocyte subsets from BCG-vaccinated donors in response to d ifferent subcellular fractions of BCG was analysed and compared with that o f not sensitized subjects. Proliferation of different cell subsets was eval uated by flow cytometric determination of bromodeoxyuridine incorporated in to DNA of dividing cells and simultaneous identification of cell surface ma rkers. Although a certain degree of variability was observed among differen t donors, after 6 days of in vitro stimulation BCG-vaccinated subjects disp layed, as a mean, a stronger blastogenic response to all the classes of ant igens compared with non-sensitized ones. PPD, culture filtrates and membran e antigens induced a predominant proliferation of CD4(+) T cells. In contra st, preparations enriched in cytosolic antigens elicited strong proliferati on of gamma delta(+) T cells which, as a mean, represented 55% of the proli ferating cells. Although to a lesser extent, proliferation of gamma delta() T cells was also elicited by preparations enriched in membrane and cell w all antigens. In response to the latter preparation proliferation of CD4(+) T cells and CD16(+)/CD3(-) (natural killer (NK)) cells was observed, as we ll. In particular, cell wall antigens were found to induce significantly hi gher levels of proliferation of NK cells compared with all the other classe s of antigens.