Effect of lindane exposure on rainbow trout (Oncorhynchus mykiss) immunity. IV. Prevention of nonspecific and specific immunosuppression by dietary vitamin C (ascorbate-2-polyphosphate).

The effect of the organochlorine insecticide lindane (gamma-hexachlorocyclohexane) administered intraperitoneally at 10 or 50 mg/kg body wt on some major immune functions of rainbow trout (Oncorhynchus mykiss) was examined. Fish were fed vitamin C as ascorbate-2-polyphosphate at a basal level (60 mg ascorbic acid-(AA)-equivalent/kg of feed) or a high level (2000 mg AA-equivalent/kg) 1 month before lindane exposure and during the whole experiment. The aim of the experiment was to determine whether dietary vitamin C is able to prevent immunosuppression due to lindane. The concentration of ascorbic acid in organs and the circulation was controlled, and the number of lindane residues in whole body was measured by gas chromatography. Nonspecific immune response was investigated through the determination of sera lysozyme and ceruloplasmin; both were significantly modified by lindane exposure while the immediate stimulating effects of vitamin C were observed. Cellular immunity was investigated by determining the number of B lymphocytes (analyzed by cytofluorometry) and their ability to proliferate with mitogens. One month after exposure to lindane (10 mg/kg) the proportion of Ig+ lymphocytes in head kidney was significantly decreased by the insecticide. Higher levels of vitamin C (2000 mg/kg) led to a significant increase in this parameter. Thus, vitamin C had a compensating effect on the number of Ig+ lymphocytes in exposed fish. Lindane at 10 mg/kg decreased the proliferation of B lymphocytes, but this was not confirmed at 50 mg/kg. Vitamin C stimulated the proliferation for the latter concentration after 2 months of intake. In lindane-exposed fish, the PMA-induced chemiluminescent response of head kidney phagocytic cells was variable from one assay to another, while most of the time vitamin C acted as a stimulant. The humoral response to Yersinia ruckeri was not modified by lindane but was significantly increased by vitamin C for 1 month after the antigen injection and thus 2 months after vitamin intake.