Thalidomide--effect on T cell subsets as a possible mechanism of action.

Thalidomide is the drug of choice in the erythema nodosum leprosum (ENL) type of lepra reaction. Lately it has been used successfully in other diseases, such as discoid lupus erythematosus, actinic prurigo, Behcet's disease, etc. However, its mechanism of action remains unknown. In patients for whom thalidomide provided relief in their disorder, the proportions of T lymphocytes and their subsets in peripheral blood were assessed by means of monoclonal antibodies. Three lepromatous leprosy patients with ENL had their T helper populations significantly increased after thalidomide therapy. A 14-year-old girl with Behcet's syndrome showed a consistent decrease in Ia+ cells throughout her three-month course of thalidomide therapy. The same findings were observed in two patients with the actinic prurigo type of polymorphous light eruption. From these results, we conclude that thalidomide may act as an immunomodulating agent on T cell subsets.