Apoptosis in Crassostrea virginica and its modulation by Perkinsus marinus

Abstract

Apoptosis has been implicated as a defense mechanism against intracellular parasites whereas the parasite-induced manipulation of host apoptosis is a means to extend survival and proliferation. Perkinsus marinus is an intracellular protozoan parasite which causes large scale mortalities in the eastern oyster, Crassostrea virginica. We studied whether apoptosis of oyster immune cells (hemocytes) is increased to counteract P.marinus infection and whether P.marinus can inhibit this increase. Our data show that following in vitro exposure of hemocytes, hemocyte apoptosis significantly increased by 45 minutes, remained elevated up till 3 hours and returned to the control levels by 4 hours. In vivo, infections of oysters with P.marinus for one day resulted in elevated apoptotic levels of hemocytes accompanied by a significant decrease in circulating hemocyte concentration. By day two, apoptosis levels returned to control, and infections in oyster tissues were clearly established. Together, these results suggest that an increase in apoptosis may be an early defense mechanism employed by oysters to control infection and P.marinus successfully establishes infection by suppressing this response. Supported by NOAA/North Carolina Sea Grant and UNC Charlotte Faculty Research Grant.