Thymus-dependent lymphocytes in leprosy. II. Effect of chemotherapy on T-lymphocyte subpopulations.

The basis of the immunological unresponsiveness seen in leprosy patients is unknown. Untreated lepromatous leprosy patients display an unspecific cellular anergy which disappears with treatment, leaving an anergy specific for Mycobacterium leprae. These patients suffer from a complication, erythema nodosum leprosum, characterized by a recurrent eruption of tender skin nodules disappearing in 2 to 3 days. These nodules show a histological picture reminiscent of an Arthus reaction. Erythema nodosum leprosum can occur in untreated patients but it is more frequent in those receiving effective chemotherapy, and this has been thought to be due to massive release of antigen from the bacilli. By using monoclonal antibodies detecting different subpopulations of human peripheral blood T lymphocytes, we have shown that both borderline lepromatous leprosy patients had increased circulating suppressor cells (P less than 0.001) while the total number of T cells was within the normal range. The suppressor-cell population decreased with the duration of treatment, the change being evident at as early as 21 days. Five patients developed erythema nodosum leprosum during the study period. In all these patients the number of suppressor cells was decreased prior to the complication, increasing to original values with clinical recovery from this syndrome. There was no significant effect on T-lymphocyte subpopulations during chemotherapy of borderline tuberculoid leprosy patients. It seems that antileprosy chemotherapy precipitates erythema nodosum leprosum by interfering with immunoregulatory T cells.