Thalidomide inhibited the synthesis of IgM and IgG whereas Thalidomide + Dexamethasone and Dexamethasone alone acted as co-stimulants with pokeweed and enhanced their synthesis

Thalidomide (Thal) provides effective treatment for erythema nodosum leprosum (ENL). In combination with Dexamethasome (Dex) it is an effective treatment for multiple myeloma (MM) and Waldenström's macroglobulinemia (WM). Thal's mechanism(s) of action in the treatment of these diverse medical conditions is not known, but it could be suppression of immunoglobulin (Ig) synthesis.Mononuclear cells were stimulated with pokeweed (PWM), and treated with Thal, Thal + Dex or Dex. The cultures were assayed for IgM and IgG.The maximum synthesis was expected to occur in cultures stimulated with PWM at 0.5, 5.0 or 10 μg/ml. The test agents at 15 μM each were expected to alter the response. Compared to cultures stimulated with PWM alone, there was significantly less Ig in the cultures containing Thal + PWM, and significantly more Ig in the cultures containing Thal + Dex + PWM or Dex + PWM (Wilcoxon). The median % of maximum was 57 for cultures treated with Thal + PWM; 184 for cultures treated with Thal + Dex + PWM, and 139 for cultures treated with Dex + PWM.Thal also acted as a co-stimulant with PWM and enhanced the synthesis of IL-2, IL-6 and DNA; whereas, Thal + Dex or Dex enhanced Ig synthesis, but suppressed IL-2, IL-6 and cell proliferation.Thal's ability to suppress Ig may explain its activity in ENL, MM and WM. The enhancement of Ig by Dex does not help to explain a role for Dex alone or in combination with Thal for the treatment of MM and WM.