Submitted to: Journal of Shellfish Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/2/2011
Publication Date: 10/29/2011
Citation: Anderson, R., Gulnihal, O., Kingsley, D.H., Maureen, S.A. 2011. Oyster hemocyte mobilization and increased adhesion activity after beta glucan administration. Journal of Shellfish Research. 30(3):635-641. Interpretive Summary: Hemocytes, or oyster blood cells, perform a number of critical biological functions. They transport nutrients, facilitate wound repair, and have a number of important digestive and immune functions. In this manuscript, the ability to activate hemocytes against pathogens is mimicked by administration of bacterial exposure using beta-1,3 glucans which mimic cell wall components of bacterial cells. Results show that hemocytes do respond to these glucan preparations inferring that oyster immune responses can be boosted in response to antigenic stimulus. These studies may lead to a better understanding of the oyster immune system and possibility a means of enhancing disease resistance in shellfish stocks.
Technical Abstract: In the eastern oyster (Crassostrea virginica) hemocytes are important effector cells for maintenance of defense against pathogenic microorganisms. Various forms of ß-glucans have been suggested for use in shrimp and fish aquaculture because of their potential to enhance disease resistance via hemocyte activation. In order to gain insight on the effects of these compounds in mollusks, changes in circulating oyster hemocyte numbers, population profiles and adhesion were quantified after injection of Beta-1,3-glucans. These agents included zymosan A or MacroGard®, an immune stimulant suggested for aquaculture applications. Results were compared to those from vehicle-injected control oysters at daily intervals for 72 hours. MacroGard® produced a rapid (24 hr) elevation of total circulating hemocytes, which remained significant for 72 hours; zymosan A stimulation of this response was not statistically significant. MacroGard® administration resulted in a sustained increase in percent granulocytes in circulation; zymosan also produced an increment in the numbers of granulocytes that became significant by 72 hours. Granulocytes are considered to be the most immunologically active hemocyte subclass. Both Beta-glucans preparations promoted hemocyte aggregation at days 1-3 post injection. Analysis of avidity of hemocyte aggregation using an index of clump cellular density confirmed this observation. Hemocytic aggregation is thought to be an indicator of cell activation. These results suggest that ß-glucans can act to increase the numbers of circulating hemocytes available for defense responses, to promote long-term changes in the hemocyte profile favoring immunologically active cells, and to enhance hemocytic aggregation. Further studies of the physiological consequences of these effects of Beta-glucans on oyster hemocyte defense parameters are in progress.