Immune response, MT and HSP70 gene expression, and bioaccumulation induced by lead exposure of the marine crab, Charybdis japonica

In order to understand the mechanisms of the toxicity of lead (Pb) on invertebrates, the immunotoxic effects of Pb in the marine crab, Charybdis japonica, were evaluated in the present study. The crabs were exposed to 0.066, 0.132, 1.318, 2.636, 6.590, and 13.181 μM of lead acetate and a control over 30 days, and the hemolymph was sampled terminally for testing the immunity-related indices, including total hemocyte count (THC), hemocyanin content, the activities of the phenoloxidase (PO) and lysozyme (LSZ). In addition, tissue samples were collected from the hepatopancreas, gill, muscle and ovary after 30 days of exposure for detecting the Pb accumulation in the major organs. The gene expression profiles of metallothionein (MT) and heat shock protein 70 (HSP70) in the hepatopancreas of C. japonica upon exposure to lead acetate over 96 h were also analyzed. The results showed a decline in the majority of the immunity-related parameters after an initial rise, and their levels were significantly lower in the treatment groups compared with those in the control, except in the group exposed to 0.066 μM of lead acetate for 30 days. Furthermore, a significant negative correlation was observed between the lead acetate concentration and the hemocyanin content, the activities of PO and LSZ (P<0.01). The expression levels of MT and HSP70 genes were rapidly induced, reaching a peak level after 12 and 24 h of exposure, respectively, and remained at a significantly higher level than the control after 96 h of exposure. It was also observed that the distribution pattern of Pb in the tissues of exposed crabs was in the order of gill > hepatopancreas > ovary and muscle, and exhibited a concentration-dependent response. Taken together, the results revealed that Pb exposure induced the immunosuppression of C. japonica and resulted in bioaccumulation, which could subsequently increase the disease susceptibility and threaten the food safety.