Effect pf preincubation on the proliferative response to antigen by cells from leprosy patients and healthy controls

One of the postulated mechanisms contributing to the selective T-cell hyporesponsiveness in patients with leprosy is receptor blockade, the characteristic feature of which is reversibility following preincubation of cells in vitro. To test this hypothesis, peripheral blood mononuclear cells (PBMC) obtained from 17 leprosy patients and 10 healthy Mantoux-positive and -negative controls were cultured freshly or after a period of preincubation in serum-containing medium, and the proliferative responses to Mycobacterium leprae, BCG, and streptokinase-streptodornase (SKSD) were measured. On the basis of the response to M. leprae, the leprosy patients could be divided into low, intermediate and high responders. Preincubation for 2-16 hr resulted in enhanced proliferation by cells from moderate responders, but not from low or high responders. Although the effect was serum dependent, it was neither antigen specific nor was it confined to cells from leprosy patients. Thus, an increase in response to both the crossreactive and unrelated antigens BCG and SKSD occurred, and the same trend was observed when cells from healthy controls were preincubated in serum-containing medium. Furthermore, cells from different individuals displayed varying responses to different antigens following preincubation, suggesting that the effect of this step was neither confined to isolated individuals nor to particular antigens. The addition of pronase to the preincubation step did not further enhance the response to antigen over and above that obtained with preincubation alone. It was therefore concluded that the enhanced proliferative response to antigen following preincubation was an in vitro phenomenon dependent upon the culture conditions employed, was not specific to leprosy, and was not related to receptor blockade