The knowledge about the direct effects of heavy metals on fish leucocytes is still limited. We investigate the in vitro effects of heavy metals (Cd, Hg, Pb or As) on oxidative stress, viability and innate immune parameters of head-kidney leucocytes (HKLs) from European sea bass (Dicentrarchus labrax). Production of free oxygen radicals was induced by Cd, Hg and As, mainly after 30 min of exposure. Cd and Hg promoted both apoptosis and necrosis cell death while Pb and As did only apoptosis, in all cases in a concentration-dependent manner. Moreover, expression of genes related to oxidative stress and apoptosis was significantly induced by Hg and Pb but down-regulated by As. In addition, the expression of the metallothionein A gene was up-regulated by Cd and Pb exposure though this transcript, as well as the heat shock protein 70, was down-regulated by Hg. Cd, methylmercury (MeHg) and As reduced the phagocytic ability, whereas Hg and Pb increased it. Interestingly, all the heavy metals decreased the phagocytic capacity (the number of ingested particles per cell). Leucocyte respiratory burst changed depending on the metal exposure, usually in a time- and dose-manner. Interestingly, the expression of immune-related genes was slightly affected by Cd, MeHg, As or Pb being Hg the form producing the greatest alterations, which included down-regulation of immunoglobulin M and hepcidin, as well as the up-regulation of interleukin-1 beta mRNA levels. This study provides an in vitro approach for elucidating the heavy metals toxicity, and particularly the immunotoxicity, in fish leucocytes.
Keywords: Apoptosis; European sea bass; Heavy metals; Oxidative stress; Phagocytosis; ROS.
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