Different responses of monocytes and active T lymphocytes to in vitro challenge of purified protein derivative (PPD) in patients with active tuberculosis and healthy tuberculin reactors.

In order to ascertain the roles of phagocytes and T lymphocytes in the defense of tuberculous infection, 21 cases of healthy tuberculin reactors and 45 cases of active tuberculosis were studied with regard to the expression of Fc and complement receptors on phagocytes and changes of surface markers of lymphocytes after in vitro incubation with purified protein derivative (PPD). After PPD stimulation, the monocytes with Fc and complement receptors tended to increase in tuberculin-positive but not in tuberculin-negative patients in patients. Thus the failure of the monocytes to be activated by PPD in vitro correlates with negative skin test in vivo and the inability of the lymphocytes from patients to respond to in vitro PPD activation with increased active T lymphocytes may account for the establishment of tuberculous infection after exposure to virulent tubercle bacilli.