Evaluation of immune function in juvenile turbot Scophthalmus maximus (L.) exposed to sediments contaminated with polychlorinated biphenyls

Abstract

Turbot of approximately 2·3g body weight were held in the laboratory on sediment which had been taken from a clean marine site, then either spiked with a set dose of polychlorinated biphenyls (PCBs) or left unspiked as the reference sediment. Serum antibody levels were measured at week 10 of exposure to the sediment (8 weeks after primary immunisation with Keyhole Limpet Haemocyanin [KLH] in solute) and again at week 18 of exposure (8 weeks after secondary immunisation with KLH in Freund's Complete Adjuvant [FCA]). All fish grew well and blood leucocyte counts were similar in all groups. There was no difference in anti-KLH antibody levels between the fish on the PCB-spiked sediment and those on the reference sediment. Assays for non-specific immune responses also failed to detect differences between fish on the PCB-spiked sediments and their respective controls on the reference sediment, whether immunised or non-immunised, with one exception, i.e. it was found that in non-immunised fish, adherent leucocytes from the PCB-exposed fish at week 10 (but not at week 18) showed significantly decreased production of intracellular superoxide anion (O2−) compared with their non-exposed controls. A more marked difference in the non-specific immune parameters occurred as a result of immunisation, irrespective of the type of sediment. Thus at week 10, intracellular O2−production was lower in the immunised fish than in their non-immunised controls. Extracellular hydrogen peroxide (H2O2) was also affected, the levels being higher in immunised fish than in non-immunised fish on the reference sediment. By week 18 the total serum protein and lysozyme levels were considerably lower in the KLH-immunised groups than in their controls. The results are discussed in relation to their relevance to fish in the wild; also to the complexity of the interactions which occur during the course of an immune reaction.