Evaluation of an innate immune reaction to parasites in earthworms.

Encapsulation is an essential process of the invertebrate immune system and includes the prophenoloxidase (proPO) cascade. We present an assay for evaluating this immune response, now newly adapted to earthworms. Coelomic fluid is withdrawn and coelomocytes are stained with l-Dopa. We studied assay repeatability and the correlation between number of PO-active cells and infection level of the parasitic protozoan Monocystis sp. in the earthworm Lumbricus terrestris. Our study showed high assay repeatability although the expected negative relationship between PO-active coelomocytes and parasite load was not observed; yet a suggestion toward a positive relationship was detected. This finding is contrary to previous assumptions that presume coelomocyte concentrations to be the independent variable determining parasite load.