In vitro interactions between hemocytes of the eastern oyster, Crassostrea virginica Gmelin, 1791 and Cryptosporidium parvum oocysts.

It was demonstrated by an in vitro slide phagocytosis assay that hemocytes of the Eastern oyster, Crassostrea virginica Gmelin, 1791 are capable of rapid recognition and internalization of infectious Cryptosporidium parvum (AUCP-1 strain) oocysts. The incubation of hemocyte monolayers (8.5 x 10(4) cells) that had received 6.8 x 10(5) or 3.4 x 10(5) oocysts was arrested at 5, 15, 30, 60, 90, and 120 min and the oocytes detected by acid-fast stain and immunofluorescent antibody (IFAT). An average of 20.5, 38.3, 50.2, 58.9, 69.0, and 75.0% oocysts were phagocytosed after 5, 15, 30, 60, 90, and 120 min, respectively. The intensity of fluorescence of phagocytosed oocysts significantly decreased over time (P < 0.01), and their round shape was altered. The number of cells containing oocysts and the mean number of ingested oocysts (range: 1.2-4.5 per cell) increased significantly over time (P < 0.01), whereas the numbers of nonphagocytosed oocysts that were adherent to the glass slides significantly decreased (P < 0.05). By extrapolation, the results indicate that Cr. virginica is capable of internalizing up to 6.4 x 10(6) Cryptosporidium oocysts per ml of its hemolymph.