title: Immunomodulation by the interactive effects of cadmium and hypercapnia in marine bivalves Crassostrea virginica and Mercenaria mercenaria.
abstract: Estuarine organisms are exposed to multiple stressors including large fluctuations in partial pressure of carbon dioxide (P2CO) and concentrations of trace metals such as cadmium (Cd) that can affect their survival and fitness. Ocean acidification due to the increasing atmospheric (P2CO) leads to a decrease in pH and shifts in the carbonate chemistry of seawater which can change bioavailability and toxicity of metals. We studied the interactive effects of (P2CO) and Cd exposure on metal levels, metabolism and immune-related functions in hemocytes of two ecologically and economically important bivalve species, Mercenaria mercenaria (hard shell clam) and Crassostrea virginica (Eastern oyster). Clams and oysters were exposed to combinations of three (P2CO) levels (∼400, 800 and 2000 μatm (P2CO), corresponding to the present day conditions and the projections for the years 2100 and 2250, respectively) and two Cd concentrations (0 and 50 μg l(-1)) in seawater. Following four weeks of exposure to Cd, hemolymph of both species contained similar Cd levels (50-70 μg l(-1)), whereas hemocytes accumulated intracellular Cd burdens up to 15-42 mg l(-1), regardless of the exposure P2CO. Clam hemocytes had considerably lower Cd burdens than those of oysters (0.7-1 ng 10(-6) cells vs. 4-6 ng 10(-6) cells, respectively). Cd exposure suppressed hemocyte metabolism and increased the rates of mitochondrial proton leak in normocapnia indicating partial mitochondrial uncoupling. This Cd-induced mitochondrial uncoupling was alleviated in hypercapnia. Cd exposure suppressed immune-related functions in hemocytes of clams and oysters, and these effects were exacerbated at elevated (P2CO). Thus, elevated (P2CO) combined with Cd exposure resulted in decrease in phagocytic activity and adhesion capacity as well as lower expression of mRNA for lectin and heat shock protein (HSP70) in clam and oyster hemocytes. In oysters, combined exposure to elevated (P2CO) and Cd also led to reduced activity of lysozyme in hemocytes and hemolymph. Overall, our study shows that moderately elevated (P2CO) (∼800-2000 μatm P2CO) potentiates the negative effects of Cd on immunity and thus may sensitize clams and oysters to pathogens and diseases during seasonal hypercapnia and/or ocean acidification in polluted estuaries.
authors.affiliation: Department of Biological Sciences, University of North Carolina at Charlotte, Charlotte, NC, USA.
authors.forename: Anna V
authors.initials: AV
authors.lastname: Ivanina
authors.affiliation: Department of Biological Sciences, University of North Carolina at Charlotte, Charlotte, NC, USA.
authors.forename: Chelsea
authors.initials: C
authors.lastname: Hawkins
authors.affiliation: Department of Biological Sciences, University of North Carolina at Charlotte, Charlotte, NC, USA. Electronic address: isokolov@uncc.edu.
authors.forename: Inna M
authors.initials: IM
authors.lastname: Sokolova
mesh_terms: D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D002245:Carbon Dioxide / Q000633:toxicity*; D049896:Crassostrea / Q000187:drug effects* / Q000276:immunology; D006434:Hemocytes / Q000187:drug effects / Q000276:immunology; D056747:Immunomodulation / Q000187:drug effects; D049891:Mercenaria / Q000187:drug effects* / Q000276:immunology; D012623:Seawater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; D002104:Cadmium; D002245:Carbon Dioxide
keywords: Bivalves; Hemocytes; Immune function; Metals; Ocean acidification