Age-specific immunocompetence of the earthworm Eisenia andrei: exposure to methylmercury chloride.

Little information with regard to the sensitivity of the immune system of earthworms to toxicants is currently available. To that effect, we evaluated the yield of coelomocyte immune cells and their phagocytosis potential for four different stages of development of the earthworm Eisenia andrei both for in vitro and in vivo exposure. Cell viability was similar among size classes; extruded cell yield increased from 0.7 x 10(6) cells/worm in the smallest size class to 2.9 x 10(6) cells/worm in the largest size class. The proportion of phagocytically active cells was lower in the smallest groups but not different among the other three groups. Phagocytosis increased incrementally for the first three age/weight groups. The absolute phagocytosis level of the hatchling worms is significantly lower than that of the adult worms. The in vivo filter paper exposure of the mature worms showed a hormetic stimulation of 200-300% of phagocytosis and no significant effects on the phagocytosis potential of the hatchlings. The absolute response of coelomocytes from younger worms was significantly lower and the estimates of lethal mercury concentrations showed the hatchling worms to be roughly three times more sensitive than mature worms.