In vitro lymphocyte reactivity during depression of tuberculin hypersensitivity by 6-mercaptopurine.

Administration of 6-mercaptopurine suppressed appearance of tuberculin skin test reactivity for up to 6 weeks after mycobacterial injection. Lymphocytes obtained during the period of suppressed tuberculin reactivity exhibited normal in vitro proliferative responses to tuberculin, suggesting that the drug may not be qualitatively affecting function of immunologically competent cells.