RESUMO
Endogeic earthworm Metaphire posthuma (Valliant, 1868) is a common biological component of the tropical soil of India and other countries. The species is reported to influence fertility and porosity of soil and bear a high composting potential. Intensive agricultural, industrial, and mining activities increase the amount of toxic metals in soil causing physiological adversity in earthworm and other biotic components in soil. Coelomocytes, the chief immunoeffector cells of earthworm, perform diverse physiological functions under the challenge of toxins and pathogens. The experimental earthworms collected separately from soils with agricultural and tannery activities were subjected to quantitation of prooxidation and antioxidation parameters for estimation of oxidative stress. Total count, cellular aggregation, generation of reactive oxygen species (ROS), superoxide anion, nitric oxide, activities of phenoloxidase, superoxide dismutase, catalase and glutathione-s-transferase, and amount of total protein were estimated in the coelomocytes of M. posthuma as experimental end points of toxicity screening. Concentrations of cadmium, chromium, lead, and mercury were determined in the soil samples to assess the degree of toxic contamination. The increase in the amount of prooxidants and decrease in the activities of antioxidant enzymes indicated the signs of oxidative stress in the coelomocytes of the organism. Aggregation of circulating coelomocytes is considered as an immune response involved in pathogen encapsulation response as reported in many invertebrates. Decrease in coelomocyte aggregation in earthworm collected from contaminated sites suggested a state of inappropriate shift of the innate immune status. Toxin-induced oxidative stress and reductions in cell aggregation response are the signs of immunocompromisation of M. posthuma. Present findings bear a prospect of this experimental species as an indicator of soil pollution.
