Suppressor T-cells in BCG-infected mice.

Specific pathogen-free B6D2 hybrid mice were infected with high (10(8) cells, intravenous), moderate (10(6) cells, intravenous), and low 10(3) cells, aerogenic) doses of viable BCG Pasteur. The growth of the BCG in the lungs and spleens of the three groups was followed over a 90-day period and correlated with the level of tuberculin hypersensitivity. Spleen cells were harvested from the three groups of mice at increasing time intervals and filtered through nylon wool to remove adherent cells, and the level of blast transformation after exposure to phytohemagglutinin and purified protein derivative was determined. Early in the BCG infection both the high- and the intermediate-dose groups showed enhanced thymidine incorporation by the spleen cell cultures, followed by a profound depression late in the infection. At this time, both groups of mice were anergic to purified protein derivative injected into footpads. Cell mixing studies demonstrated the presence of a population of suppressor cells in the spleens of the anergic animals. The suppressive abilities of these cells would be ablated by treatment with anti-Thy-1 antiserum and complement. The aerogenically infected mice were unresponsive to purified protein derivative but showed no evidence of suppressor T-cells. The lack of tuberculin sensitivity in these mice seemed to be due to a lack of sensitized T-cells in the spleen rather than to active immunosuppression.