Comparative study of skin reactions in leprosy patients to M. leprae-lepromin and to ICRC-in, an antigen from cultivable acid-fast bacilli from M. leprae isolated from lepromatous nodules.

Skin test antigens (Dharmendra type) were prepared from fresh M. leprae (lepromin) and from a culture of strain C-44 ICRC bacilli (ICRCin) grown 'in vitro' from M. leprae isolate from lepromatous nodules. Comparative study of skin reactivity to lepromin and ICRCin--both "early" and "late" reactions in 76 leprosy patients was conducted. In 29 lepromatous (LL) cases, 25 exhibited totally negative reaction at the end of third week. In tuberculoid (TT) 22 and 23 out of 31 were positive (greater than 4.5 mm) at 3 weeks to lepromin and ICRCin respectively. In the 16 BB group, the reactions were comparable in the same patient. The cellular reaction in tuberculoid cases consisted of lymphocytic infiltration, epitheloid giant cells and Langhan type cells and indistinguishable from each other. These data with characteristic total lack of reaction in 25/29 lepromatous leprosy cases and identical cellular reaction in TT patients, provide strong evidence that ICRC bacillus strain C-44 is antigenically identical with M. leprae.