Quahog Parasite Unknown (QPX) is a protistan parasite of hard clams, Mercenaria mercenaria, and has caused significant mortality of wild and cultured clams in the northeastern United States. The QPX organism is thought to be facultative and typically causes disease when there is an environmental stress that reduces the ability of clams to fight infection. One environmental concern of importance is natural and synthetic estrogen contamination. Natural and synthetic estrogens are endocrine disrupting compounds (EDCs) that have been found in freshwater, estuarine, and marine environments thus representing a potential hazard for aquatic species. Exposure to contaminants such as estrogen could compromise immune function and progressively lead to infectious diseases such as QPX. This study was designed to investigate the effects of synthetic estrogen, 17α-ethynyl estradiol, on QPX-induced immune responses in M. mercenaria. Clams were separated into 4 groups: control, estrogen (125 ng/L), QPX (New York strain, 8BC7), and estrogen/ QPX, and were maintained at 18°C for 2 months. QPX- specific cell- mediated and humoral defense parameters were assessed after 1 and 2 months. Measured parameters included total and differential hemocyte counts (flow cytometry), reactive oxygen species (ROS) production (NBT colorimetric assay), phagocytosis activity (fluorescent bead assay), and lysozyme activity and protein concentration in plasma (spectrophotometric assay; BCA protein assay).
Results/Conclusions
Results demonstrated a statistically significant decrease in ROS production within the EE/QPX treatment group. The cell mediated mechanism of phagocytosis showed a statistically significant increase in phagocytic capacity within the QPX treatment group. Results demonstrated the immuno-suppressive activities of synthetic estrogen and QPX parasitism. Total hemocyte counts decreased from the first month to the second month of exposure within the experimental groups: EE, QPX, and EE/QPX. There was also a decrease in the number of granulocytes from the first to second months within groups, QPX and EE/QPX. Estrogen also showed stimulatory effects by increasing the number of granulocytes with longer exposure time. Our results will contribute to a greater understanding of QPX infection dynamics as well as the potentially negative indirect effects of estrogen contamination leading to QPX infection in M. mercenaria. Our results also suggest the feasibility of using bivalves as indicator species of estrogen contamination.