Incorporation of ³H-thymidine in Mycobacterium leprae within differentiated human macrophages

Abstract

The factors influencing the incorporation of ³ H-thymidine (³ H-Tdr) in the DNA of Mycobacterium leprae within macrophages derived from human blood have been evaluated. Fifty strains of M. leprae derived from skin nodules of patients with lepromatous leprosy were studied for their ability to incorporate ³ H-Tdr. Control macrophages of the same donor maintained alone, or with autoclaved M. leprae, showed low levels of baseline ³ H-Tdr incorporation. During a 15-day period of pulsing, 27 of the M. leprae strains incorporated ³ H-Tdr at levels of 216-2834% of the incorporation by control cultures. Significant incorporation was observable by the second week of culture and cumulative increases occurred by the third week. A 24-h pulse with ³ H-Tdr was inadequate for a detectable increase. A minimal duration of 4-5 days of continuous pulsing was required to obtain a significant increase in the incorporation of ³ H-Tdr. Of the 50 M. leprae strains, 23 (46%) failed to incorporate the radiolabel. This failure was apparently not related to differences in the disease status of patients, to the transport conditions for the biopsies, to morphological indices of the extracted M. leprae or to the origin of the host macrophages.