Figure 4. . . Three-dimensional (3-D) INT-407 intestinal cell aggregates do not express the histo-blood group antigens important for Norwalk virus (NV) attachment. Monolayer (ML) INT-407, 3-D INT-407 aggregates, and Caco-2 ML (positive control) were labeled with 2 different H type 1 (BG-4 and UEA-1) antibodies and with antibodies against H type 2, Leb, and Lea (green) and imaged by confocal immunofluorescence microscopy. Nuclei were counterstained with 4',6-diamidino-2-phenylindole (blue). Scale bars = 50 μm.