Lysozyme activity in earthworm (Lumbricus terrestris) coelomic fluid and coelomocytes: Enzyme assay for immunotoxicity of xenobiotics

Lysozyme activity in earthworm (Lumbricus terrestris) coelomic fluid and coelomocytes appears sufficiently sensitive for use as a nonmammalian biomarker to detect toxic effects of sublethal body burdens of Cu2+ (28.5 ± 2.67 and 73.1 ± 5.68 μg/g dry mass). Lysozyme, a phylogenetically conserved enzyme, is capable of bactericidal activity via action on peptido-glycan of gram-positive bacterial cell walls and functions as a component of an organism's innate antimicrobial defense mechanism. Coelomic fluid and coelomocyte lysozyme activities, which exhibited temperature-response patterns similar to those of human saliva, plasma, serum and leukocyte extracts, were sensitive to Cu2+ exposure. Lysozyme activity of coelomic fluid and coelomocyte extracts from earthworms exposed for 5 d to CuSO4, using filter paper contact exposure, decreased with increasing sublethal Cu2+ concentrations of 0.05 and 0.1 μg/cm2. Compared to controls, coelomic fluid lysozyme activity was suppressed significantly at both exposure concentrations, whereas coelomocyte extract lysozyme activity was suppressed significantly at the 0.1-μg/cm2 exposure concentration. Low inherent natural variability and sensitivity to sublethal Cu2+ body burdens indicate that lysozyme activity has potential as a biomarker for assaying immunotoxicity of metals.