Structure-activity relationship of phenolic compounds (phenol, pyrocatechol and hydroquinone) on natural lymphocytotoxicity of carp (Cyprinus carpio).

We have tested the effects of phenol and two diphenols (pyrocatechol and hydroquinone) on a non-specific immune response, i.e. the natural cytotoxic activity, of the carp. After a 12-day exposure of fish, at a concentration of 0.1 mg/l, hydroquinone appeared to exert the most immunotoxic effect in vivo. In vitro, after a preincubation of 1 h, phenol (10(-2) M), pyrocatechol (4.25 x 10(-4) M) and hydroquinone (4.25 x 10(-5) M) decreased the natural cytotoxic activity of lymphoid cell suspension. In vivo and in vitro experiments show that hydroquinone is the most toxic compound, whereas diphenols are more toxic than phenol. These results demonstrate that the study of immune systems can reveal the presence of toxic substances with varying degrees of toxicity. Also, the position of a second hydroxic group on the benzonic nucleus seems to influence the compound toxicity.