The chemiluminescence response of bivalve haemocytes: utility in screeningfor immunomodulators and as a biomarker

Resistance to infectious diseases in bivalves depends primarily on the vigo ur and efficacy of haemocyte-dependent antimicrobial defence mechanisms. Li ke other phagocytes, haemocytes seem to rely on oxygen-independent (lysosom al hydrolases, lysozyme) and oxygen-dependent (reactive oxygen species) mec hanisms to destroy ingested microorganisms. The generation of cytotoxic oxy radicals by haemocytes can be precisely quantified by means of a simple che miluminescence (CL) assay using luminol or other CL probes. Tributyltin (TB T), and other environmental contaminants, at sublethal levels, will produce dose-dependent suppression of CL activity in haemocytes exposed in short-t erm, in vitro assays. Presumably, this suppression would find expression as impaired host defence capability In fact, TBT has been shown to exacerbate progression and lethality of Perkinsus marinus infections in the oyster, C rassostrea virginica. This suggests that CL assays on haemocytes exposed in vitro to single agents or complex mixtures might be useful in screening fo r aquatic immunomodulators. Statistically significant alterations in CL res ponses of haemocytes withdrawn from bivalves exposed to xenobiotics in the laboratory or field are more difficult to identify because of high interani mal variation; however, the use of haemocyte CL as a biomarker of effect me rits further investigation.