Immunosuppressant activity of the ansamycins.

The immunosuppressive effect of four analogues of rifampin and two streptovaracins on cell-mediated immunity has been determined. Tuberculin hypersensitivity in the footpads of immunized mice was inhibited by three of the rifampin analogues and by both streptovaracins. The observed in vivo immunosuppressive activity of the compounds tested was not correlated with their in vitro activity against mycobacterial growth but was associated with their toxicity in mice. These data indicate that some of the analogues of rifampin and the streptovaracins can significantly suppress cell-mediated immunity and suggest that other ansamycins may have significant immunosuppressant activity.