Incorporation of Tritiated Thymidine by Leprosy Bacilli in Cultures of Human Lepromatous Macrophages

Abstract

Mycobacterium leprae, which circulates in mononuclear phagocytes in the blood of patients with untreated lepromatous leprosy, has never been successfully cultivated in an artificial medium and can presently be studied only in animal models. A method for the evaluation of the in-vitro, DNA-synthetic activity of M. leprae was devised. Monocytes from the blood of bacteremic patients with lepromatous leprosy were cultivated in vitro and exposed to tritiated thymidine of high specific activity. Leprosy bacilli within the developing macrophages were shown by radioautography to incorporate tritiated thymidine. Consistent with the known 14-day generation time of M. leprae in animal models, relatively few leprosy bacilli were engaged in DNA synthesis at any given time. This technique provides an in-vitro approach to the evaluation of M. leprae within its natural host cell, the human macrophage.