The effects of azathioprine and levamisole on lymphocyte stimulation.

Azathioprine at 10 micrograms per ml caused approximately a 50% inhibition of phytohaemagglutinin (PHA), purified protein derivative (PPD) or Veillonella induced in vitro lymphocyte stimulation. This suppression was significantly reduced in lymphocyte cultures from patients undergoing an eight week course of levamisole therapy. Azathioprine-induced suppression was also reversed when culturing lymphocytes in the presence of levamisole. On the other hand, levamisole in vitro failed to reverse the azathioprine suppression of cord blood lymphocyte responses.