Radiometric Macrophage Culture AssayforRapidEvaluation ofAntileprosy Activity ofRifampin

strain of Mycobacterium leprae weremaintained for2and3weeks, respectively, inmurine andhumanmacrophages inthepresenceof[3H]thymidine. Ofthesestrains, 27 showedsignificant incorporation oftheradiolabel incultures oflivebacilli as compared withcontrol cultures ofheat-killed bacilli ofthesame strain. Consistent andsignificant inhibition of[3H]thymidine uptake was observed inM. leprae resident cultures with3to200ng ofrifampin permlas compared withsimilar cultures without thedrug. Ingeneral, an increase inpercent inhibition was seen from3to20ng/ml, withmarginal increases at40,50,and100ng/ml. M. leprae strains appeartoberemarkably susceptible tothisdrugintheinvitro assay. Inrecent years, ourlaboratory hasdeveloped arapid invitro radiometric assay fortheevaluationoftheviability ofMycobacterium leprae. Overa2-to3-weekperiod, 150human-derived M.leprae strains maintained inmouseperitonealandhumanmonocyte-derived macrophage cultures showedsignificant uptake of[3H]thymidineascompared withparallel cultures ofheatkilled bacilli obtained fromthesameskinbiopsy (16, 20). Thattheincorporation oftheradiolabel wasinthebacilli andnotinthehostcells was shownbyDNaseexperiments (8, 20). Thisassay hasbeeneffectively usedtostudy theeffect of dapsone (4,4'-diaminodiphenyl