Lepromin and Tuberculin Reactivity in Adults not Exposed to Leprosy

A group of 73 adult male volunteers was skintested with lepromin, tuberculin and mumps antigen. Eighteen of them were later tested with candidin, trichophytin, blastomycin, coccidioidin and histoplasmin. All of the men had late (Mitsuda) reactions to lepromin greater than 4 mm in diameter and many of them had quite strong reactions. The sensitivity to tuberculin had little influence on the size of the lepromin reactions, thus indicating that in this group the reactivity to lepromin had not often arisen from exposure to tubercle bacilli or other mycobacteria. Since they were residents of non-endemic areas of the United States, it was very unlikely that any of the men had been exposed to leprosy bacilli. Thus, although lepromin reactivity was well developed in this group of men, its origin is unexplained.