Experience and lessons from the use of lepromin and Mycobacterium leprae-specific serology

Skin testing with lepromin, which produces a delayed-type hypersensitivity reaction, has been used in the classification of leprosy, and a good correl ation has been found between immunological status and the reaction to lepro min. In addition, the prognostic value of the lepromin test has been demons trated. More recently, skin testing with two soluble antigens of Mycobacter ium leprae showed no difference of the mean size of the reaction between ho usehold contacts and non-contacts, indicating that these antigens are not u seful for the diagnosis of leprosy. This and other evidence points to the n eed for a better skin test antigen capable of detecting infection of indivi duals by M. leprae. Whereas serological assays for antibodies against both PGL-1 and the 35 kDa antigen of M. leprae have been found to yield positive results in 90-100% of patients with lepromatous (BL/LL) leprosy, these ass ays fail to identify 40-60% of patients with tuberculoid (BT/TT) leprosy, b ecause of the presence of only an insignificant level of antibody against c omponents of M. leprae in these patients' serum, although, in many BT patie nts, antibody signal could be detected in the local lesions. These data ind icate that there remains a need for a specific diagnostic test for leprosy.