Binding of GII-4 VLPs to carbohydrate receptors was examined by the histo-blood group antigen (HBGA) binding assay as described by others [18] , with slight modifications. Briefly, VLPs were coated at 50 ng/well, and synthetic biotinylated H type 3 and Lewis b histo-blood group carbohydrates (Lectinity Holdings Inc. Moscow, Russia) were used in serial threefold dilutions, starting from 6 lg/ml. Wells lacking the synthetic carbohydrates were used as a negative control.