Reference: Bio! Bull 192: 62-72. (February. 1997) Effects of Common Estuarine Pollutants on the Immune Reactions of Tunicates DAVID RAFTOS AND AIMEE HUTCHINSON School of Biological Sciences, Macquarie University, North Ryde. NSW, 2109, Australia Abstract. Tunicates are filter-feeding estuarine and marine animals that are frequently exposed to chronic environmental pollution. This study demonstrates that exposure to low-level (i.e., below the threshold of acute lethality) contamination with tributyltin, creosote, and copper can have substantial effects on natural immune reactions in tunicates. Sublethal doses of toxicants ad-ministered either in vitro or in vivo profoundly affected phagocytosis, cellular cytotoxicity, and hematopoietic cell proliferation. Effects were not always inhibitory, and responses often varied depending on the route of toxi-cant administration. The data suggest that pollutants can activate cascades of cellular processes and compensatory mechanisms, as well as directly inhibiting some of the responses tested. Some evidence indicates that toxicants exert their effects by altering the relative frequencies of circulatory hemocytes. Introduction Marine invertebrates can be profoundly affected by aquatic pollution. Detrimental effects have been identi-fied using tests for acute lethality (e.g., 96-h LD 5() ), toxi-cant bioaccumulation, anatomical and biochemical ab-erration, or altered biodiversity and abundance (Giam and Ray, 1987; Landis and Yu, 1995; Peakall, 1992). However, there is relatively little information regarding the effects of environmental contamination on natural immune reactions in invertebrates, even though modu-lation of the immune system may dramatically alter pop-ulations by affecting their resistance to infection ( Ander-Received 17 May 1995; accepted 24 October 1996. Abbreviations: FSW, filtered seawater; MAC. marine anticoagulant; MS. marine saline; PAH. polycyclic aromatic hydrocarbon; RRBC. rabbit red blood cells; TBT. tributyltin; TBS. Tris-buffered saline. son el ai, 1990; McCarthy and Shugart, 1990; Roales and Perlmutter, 1977; Sarot and Perlmutter, 1976; Steb-bing. 1985). Some evidence suggests that the effects of decreased disease resistance resulting from low-level, chronic pollution may not be reflected accurately in as-says that test acute lethality. For instance, heavy metal or polychlorinated biphenyl contamination in worms can significantly inhibit lysozyme activity, wound healing, phagocytosis, rosette formation, and tissue transplanta-tion rejection at concentrations that are not acutely le-thal (Cooper and Roch, 1992; Fitzpatrick et ai. 1992; Rodrigues-Grau et ai, 1989). The aim of the current study is to demonstrate that subacute contamination with three common estuarine pollutants the antifouling agents tributyltin (TBT), copper, and creosote can significantly affect the immu-nological defenses of tunicates. Tunicates (Urochordata, Ascidiacea) are aquatic filter-feeding invertebrates that are ubiquitous components of estuarine and coastal ma-rine systems (Berrill, 1950; Goodbody, 1974). They oc-cur in large populations on marinas, moorings, and wharves that are often subjected to chronic pollution, particularly from antifouling treatments. The effects of pollution are likely to be compounded in tunicates by their filter-feeding lifestyle. Large volumes of potentially polluted water pass over the sensitive endothelial sur-faces of the pharynx (up to 1 00 1 of water per day), greatly increasing the propensity of tunicates to absorb toxicants (Goodbody, 1974). Here, we test the effects of toxicants on a number of well-characterized assays of immunological reactivity in tunicates. Those assays quantify hemopoietic cell prolif-eration (Raftos and Cooper, 1991; Raftos et ai. 1991), phagocytosis (Beck et ai, 1993: Kelly et ai, 1993), and cellular cytotoxicity (Parrinello et ai, 1993; Peddie and Smith, 1993, 1994). Tunicates lack adaptive antipatho-62
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