RESUMO
Many investigators have evaluated the influence of genetic constitution on the susceptibility to leprosy in studies linked to different types of research. To determine the possible existence of a family trait linked to the lymphoproliferation and to lepromin reactivity we studied the blastogenic response to phytohaemagglutinin, lepromin and M. leprae and the Mitsuda's reaction in leprosy patients and their unaffected sibs. Sixty-eight individuals were studied, 34 were leprosy patients (17 lepromatous and 17 tuberculoid leprosy) and the remaining were their sibs previously matched by sex and age. The indices of blastogenesis and lepromin reactivity were lower in lepromatous than in tuberculoid patients, that confirmed the immunological polarity of the two types of leprosy. Both the lymphoproliferation and Mitsuda's reaction results suggest different cell immune responses in leprosy patients and their unaffected sibs, so that the hypothesis of a family trait favouring the similarity of responses to these tests among sibs becomes unlikely.