Effects of cadmium on lymphocyte proliferation and macrophage activation in catfish,Ictalurus melas

The effects of cadmium (Cd) (in vitroandin vivo) on phytohaemoagglutinin(PHA)- or lipopolysaccharide(LPS)-induced lymphocyte proliferation were investigated in the catfish,Ictalurus melas. The effects of Cd on macrophage activation by Concanavallina A orSaccharomyces cerevisiae, as measured by superoxide (O2−) production, were investigated. Dose-independent (except at 2 μmCd) inhibition of T cell stimulation and dose-dependent inhibition of B cell stimulation, by lymphocytes exposedin vitroto 2–40 μmCd, was found.In vivo, 20 μg l−1Cd inhibited both PHA- and LPS-induced lymphocyte proliferation, at 4 days of exposure and throughout the duration of the experiment. During the first week of exposure, Cd significantly decreased spontaneous3H-methyl-thymidine uptake from unstimulated lymphocytes; however, 15 days after exposure unstimulated cells recovered their basal level of spontaneous thymidine uptake.In vitro2–40 μmCd enhanced O2−production by activated macrophages, while the addition of 50–100 μmCd had no significant effects.