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

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Abstract
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.

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