Lymphocyte transformation test in healthy contacts of patients with leprosy. I. Influence of exposure to leprosy within a household.

Fifty-three household contacts of lepromatous patients, 37 household contacts of tuberculoid patients, and 91 control persons were examined with the lymphocyte transformation test (LTT) for their responses to whole and sonicated antigen preparations from M. leprae, to BCG, M. avium, M. gordonae, and phytohemagglutinin (PHA). The study was carried out in the Gurage area of Ethiopia in 15 households with a leprosy patient and 15 matched control households. Household contacts of lepromatous patients showed significantly greater LTT responses to antigens from M. leprae than the controls, whereas household contacts of tuberculoid patients did not respond differently from controls. Household contacts of lepromatous patients had significantly greater responses to M. leprae antigens when the index patients were "active," i.e., highly bacilliferous, than when they were "inactive," i.e., having a low bacillary load. The degree of sensitization, as indicated by the LTT response, in different exposure groups paralleled the degree of probable infectivity of the index patient. A preparation of antigen from whole M. leprae proved to be more sensitive and more specific in the LTT than did a sonicated preparation. A significant degree of cross-reactivity was found among the various mycobacteria in their LTT responses.