Heavy metal-specific inhibition of phagocytosis and different in vitro sensitivity of heterogeneous coelomocytes from Lumbricus terrestris (Oligochaeta).

Cell viability and phagocytic activity of coelomocytes from the gastrointestinal tract of Lumbricus terrestris were examined by flow cytometry after in vitro exposure to heavy metals. Control coelomocytes were incubated for 18 h at 15 degrees C, 5% CO2, in Ca(++)-containing LBSS medium with 10(-4)-10(-9) M mercury chloride, methylmercury, cadmium chloride, zinc chloride, lead chloride or lead acetate. Heterogeneity of coelomocyte population was demonstrated by forward scatter (FSC) analysis and cytometric profile showing two different populations of type I/small (60%) and type-II/large (40%) cells. Exposure to either form of Hg, Cd and Zn was relatively highly toxic and affected both cell viability and phagocytosis, whereas Pb was relatively well tolerated by the coelomocytes. A fraction of cells within large coelomocyte population was exceptionally sensitive to the Hg-induced cytotoxicity, which did not affect, however, the relative phagocytic activity of the remaining cells. Overall, at least three different patterns of metal-specific toxicity, affecting both viability and phagocytic functions of earthworm coelomocytes, were confirmed in our in vitro studies. Further characterisation of both the target cells from heterogeneous coelomocyte population and the specific interaction of target cell-xenobiotic can possibly reduce biomonitoring problems in earthworm toxicology and immunotoxicology.