Interferon-gamma responses to candidate leprosy skin-test reagents detect exposure to leprosy in an endemic population

New tools for the detection of leprosy exposure in a community will be nece ssary for the eradication of leprosy. Candidate leprosy skin-test antigens derived from the fractionation of the leprosy bacillus into cytoplasmic and cell-wall proteins free of immune-inhibitory mycobacterial lipoglycans and carbohydrates were used in an overnight blood test to determine whether ex posure to leprosy can be detected by the production of the cytokine interfe ron gamma (IFN-gamma). Strong IFN-gamma responses were detected in leprosy contacts to both skin-t est antigens compared with control subjects from the same endemic communiti es. There was little response in patients with tuberculosis. Responses were greatest in contacts with recent leprosy exposure. The implications of the se findings for the application of these reagents in a field trial as skin tests to detect exposure to leprosy are discussed in light of the strong as sociation between overnight IFN-gamma to PPD and the tuberculin skin-test r esponses previously reported.