In vitro stimulation of lymphocytes with an antigen fraction prepared from Mycobacterium leprae and tuberculin PPD in contacts and non-contacts of leprosy patients.

An antigen fraction from Mycobacterium leprae, called MLW1, was used as stimulator in the lymphocyte stimulation test, for comparison with tuberculin PPD. The test was performed in three groups of contacts of leprosy patients with various degree of exposure: (1) close contacts, (2) healthy occupational contacts and (3) non-close contacts and, in addition, in a group of BCG vaccinated and non-exposed controls. The MLW1 preparation induced moderate to strong responses in all three groups of contacts. Although the close contact group showed the highest median responses to all three doses tested, there were no significant differences between the contact groups. At all three doses levels the non-exposed group showed markedly and significantly lower median responses than the contact groups. The responses to tuberculin PPD was markedly and significantly lower in the close contact group than in the other groups. Both when individual responses to the two antigens MLW1 and PPD are compared and when the delta ct/min' estimator is used, the results indicate that the intensity of the specific response increases with the closeness of contact with leprosy patients.