Differences in lectin-binding by hemocytes of oysters (Crassostrea virginica) from three regions and further evidence for the correlation between the presence of lathyrose and the absence of Haplosporidium nelsoni

Hemocytes collected from Crassostrea virginica (Gmelin) originating from Malpeque Bay, Canada, Galveston Bay, TX, and Church Creek, Johns Island, SC, were exposed to serial dilutions of 9 lectins and the number of agglutinated cells/100 cells was ascertained at each dilution. Also, saccharidal residues known to inhibit the agglutination of lectin-heated cells were employed to test their effectiveness. Among these, N-acetyl-D-glucosamine, D(+)-glucose, and D(+)-mannose, which usually are specific inhibitors of cell clumping mediated by the Lathyrus odoratus lectin did not have this effect. This confirms earlier studies. Hence, the nature of the hemocyte surface saccharide, designated as lathyrose for convenience, that binds to the L. odoratus lectin remains unknown. Earlier studies had suggested that the presence of lathyrose on the hemocyte surfaces of C. virginica may signal innate resistance to Haplosporidium nelsoni (Cheng et al. 1994). The results presented herein further support this hypothesis as the percentage of lathyrose-positive hemocytes was significantly higher in oysters from Malpeque Bay and Galveston Bay where H. nelsoni has never been reported than in those from Church Creek where preliminary data indicate that this pathogen occurs in approximately 4% of the oysters. There were some qualitative and quantitative differences in the binding affinities of certain lectins to hemocytes from the 3 regions. These probably reflect strain and seasonal differences