In vitro exposure of seal peripheral blood leukocytes to different metals reveal a sex-dependent effect of zinc on phagocytic activity

Although the immunotoxicity of heavy metals is well established, evaluation of their potential immunotoxicity in wildlife species is complicated by va riables that could modulate the immune response to xenobiotics under field conditions. Phagocytosis plays a key role in the mammalian immune response. The objectives of our study were to develop a method for measuring the pha gocytic activity of seal peripheral blood granulocytes, and to determine th e effects of both zinc chloride (ZnCl2), cadmium chloride (CdCl2) and mercu ric chloride (HgCl2) on this immune function of peripheral blood granulocyt es in vitro. Peripheral blood leukocytes (PBLs) mere isolated from the peri pheral blood of either harbour seals (Phoca vitulina) or grey seals (Halich oerus grypus) captured in the St Lawrence Estuary, Cells exposed for 4 h to 10(-4) M and 10(-3) M HgCl2 displayed lower phagocytic activity but this m as related to a general cytotoxic effect of HgCl2 as opposed to a specific effect on phagocytosis. Exposure of PBLs from either male or female PBLs to CdCl2 had no effect on phagocytic activity at the concentrations tested ex cept a significant decrease in cells from male harbour seals exposed to 10- 4 M, Exposure to ZnCl2 at physiologically relevant concentrations enhanced the phagocytic activity of PBLs from mature females of both species, wherea s no effect mas observed in cells from either males or immature females. In conclusion, me have developed an in vitro assay to test the effects of env ironmental contaminants on the phagocytic activity of seal PBLs, Our data i ndicate that exposure of PBLs to ZnCl2 results in a sex-dependent response and that PBLs from mature female seals are more sensitive to ZnCl2 than eit her male or immature seals. This sex-dependent response to ZnCl2 could lead to a differential sensitivity to heavy metal exposures for males and femal es seals in the field. (C) 2000 Elsevier Science Ltd, All rights reserved.