FISH THYMOCYTE VIABILITY, APOPTOSIS AND NECROSIS - IN-VITRO EFFECTS OF ORGANOCHLORINE CONTAMINANTS

The thymus is believed to be a central component of haematopoiesis and immune function in teleosts. Hence, chemically-elicited adverse effec ts to the thymus may result in immunomodulation and organ dysfunction. The objective of this research was to assess the levels of active (ap optotic) and passive (necrotic) cell death in untreated and organochlo rine treated fish thymocytes. Lake trout (Salvelinus namaycush) thymoc ytes were challenged with Aroclor 1254 (concentration range 1.5-10.5 m u g ml(-1)) and alpha, beta, gamma, delta isomers of hexachlorocyclohe xane (concentration range 10-100 mu M). The resulting maintenance or l oss of viability was assessed by cytofluorometry (expression of phosph atidylserine and exclusion of propidium iodide) and confirmed with flu orescence microscopy. The results indicate that 20-60% of thymocytes i n healthy fish undergo apoptosis, whereas thymocytes treated for 6-24 h with organochlorines exhibit increased levels of apoptotic cell deat h. This study demonstrates that given sufficient concentration, contac t time and cellular receptors, organochlorines such as Aroclor 1254 an d hexachlorocyclohexanes may induce direct or indirect toxicity, alter ed functionality, or cell death to an organ important for fish immunoc ompetence. (C) 1998 Academic Press Limited.