Antigenic trigger for type 1 reaction in leprosy.

Type 1 (reversal or upgrading) reactions occur during or after chemotherapy in around 10% leprosy patients [Int J Lepr Other Mycobact Dis 61 (1993) 8-15]. The cause of this immunological upgrading is incompletely defined, although the approximately 2-fold increased risk of reaction in patients vaccinated with Mycobacterium w suggests that infection by mycobacteria other than Mycobacterium leprae may trigger this phenomenon [Vaccine 13 (1995) 1102-1110]. We report a case of borderline lepromatous leprosy in which we studied the antigenic specificity of peripheral blood mononuclear cells immediately before, and then during, a Type 1 reaction which provides more direct evidence in favor of this hypothesis.