A single cell assay for the study of gamma-interferon formation in leprosy patients.

The number of gamma-interferon producing cells in the peripheral blood of leprosy (LL and BT) patients and controls was studied by the reversed protein A plaque assay before and after exposure in vitro to Mycobacterium leprae bacilli and Epstein-Barr virus (EBV). The level of spontaneous gamma-interferon production was significantly higher in BT patients compared to LL patients and controls. Mycobacterium leprae induced a specific gamma-interferon response in lymphocytes from BT patients and from healthy contacts whereas in LL patients and non-exposed controls the response was low or non-existing. There were no significant differences in the gamma-interferon response to EBV between the above groups.