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.