Abstract
This study shows that high methylmercury concentrations are cytotoxic for Styela plicata hemocytes, whereas sublethal concentrations affect immunocyte responses. Moreover, hemocytes exposed to the xenobiotic present a significantly enhanced phenoloxidase activity as revealed in the hemocyte lysate supernatant compared with the control. Although the cytotoxic activity of S. plicata hemocytes toward rabbit erythrocytes is a POβdependent cellβtarget reaction due to quinone products, it was significantly decreased by suitable methylmercury concentrations in the medium. The same xenobiotic concentrations decreased the hemocyte phagocytic activity toward yeast. In both the responses cellβtarget contacts could be affected by methylmercury, whereas the releasing capacity appeared to be unchanged, as indicated by hemocyte POβrelease in the medium. Finally, changes in hemocyte shape and spreading capacity were shown. On the basis of the present results, Styela plicata hemocyte responses could be an additional immunotoxicology test using a microplate method that reveals cell morphological changes and spreading capacity. Copyright Β© 2007 John Wiley & Sons, Ltd.