Niridazole-mediated modulation of suppressor cells in Wistar rats

The antischistosomal drug niridazole has been shown to inhibit inductive (Vadas and Bernard, 1981) as well as effector phases of delayed hypersensitivity (Sainis et al., 1983). Furthermore, it also abrogates help for delayed hypersensitivity in antigen-primed animals (Sainis et al., 1983). The effect of this drug on antigen-induced suppression was examined in the present studies. Profound suppression of delayed hypersensitivity to sheep erythrocytes was obtained in Wistar rats given 10(8) erythrocytes (i.v.) 6 days before the immunizing dose (2 x 10(9) erythrocytes, i.p.). When these rats were orally administered niridazole (50 mg/kg) 7 days before the tolerising dose of antigen, suppression of delayed hypersensitivity was not obtained. Splenic lymphocytes of rats given the tolerising dose 6 days earlier adoptively transferred the suppression to inbred recipients. Treatment of these afferent suppressor cells with sera from niridazole-treated unimmunized rats abrogated their function. Likewise, the efferent suppressor cells obtained from fully tolerised rats did not suppress the delayed hypersensitivity when co-transferred with immune lymphocytes, if they were pretreated with niridazole-active serum. The metabolite of niridazole present in this serum seems to impair the suppressor cells functionally. Niridazole may thus prove to be a versatile immunomodulator for effector, helper and suppressor T-cells.