Stimulation of lymphocytes by purified protein derivative: suppression by cells from human vaccinated with Bacille Calmette-Guérin.

Specific stimulation of thymus-derived cells by purified protein derivative or tetanus toxoid was inhibited by autologous lymphocytes. The lymphocytes, which were collected from healthy humans who had been vaccinated with bacille Calmette-Guérin were purified on nylon columns after removal of cells that form rosettes with sheep erythrocytes. The degree of purification of the lymphocytes was controlled by appropriate techniques.