BCG-induced suppressor T cells optimal conditions for in vitro induction and mode of action.

In vitro activation with BCG of T cells from healthy individuals vaccinated with BCG lead to the induction of suppressor cells that suppressed the proliferation of fresh T cells in response to specific antigen. Kinetics of their induction revealed that they became radioresistant by day 8 and persisted up to 18 days of the culture period. Optimal antigen and monocyte concentrations as assessed by proliferation during the induction phase also resulted in maximum suppression. The strongest suppressor activity was observed when suppressor cells were added at an early time of fresh cell activation. IL-1 production from adherent cells in response to BCG was not affected, but, IL-2 production by T-cells was considerably reduced in the presence of suppressor cells. IL-1 containing supernatants and affinity purified IL-1 exogenously added to the culture system did not affect suppression. Whereas, recombinant IL-2 partially abrogated suppression in a dose-dependent manner. Further experiments suggested that suppressor cells might have inhibited BCG induced IL-2 receptor expression on fresh T cells.