Suppression of secretory rosette formation by PCBs in Lumbricus terrestris: An earthworm assay for humoral immunotoxicity of xenobiotics

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Abstract
Research is part of an effort to develop surrogate immunoassays with the earthworm Lumbricus terrestris to assess immunotoxic potential of xenobiotics to mammals. Objective was to determine if an earthworm humoral immunoassay, secretory (S) rosette formation by coelomic leukocytes, is sensitive to a known mammalian immunotoxin, the polychlorinated biphenyl (PCB) Aroclor 1254®. Results are presented in terms of PCB exposure and tissue levels during uptake/depuration. Using 5‐d filter paper contact exposure, LC50 and LD50 were 300 m̈g/cm2 and 1,140 m̈g/g dry mass. Nominal PCB exposure concentration of 5.0 m̈g/cm2 and actual tissue levels of 76 m̈g/g dry mass were sufficient to suppress S‐rosette formation. Suppression and return of function followed PCB levels in coelomic leukocytes, the presumed site of toxicity. Compared to published mammalian data on immunoglobulin suppression by PCBs, the earthworm immunoassay appeared to be more sensitive.