This is a custom-colored model of the surface of the hemagglutinin receptor. Subunits of the receptor are colored separately by domain: (1) red and green, (2) blue and orange, (3) yellow and purple. Antibodies bind at each of the three junctions between receptor subunits. Two antibodies are attached to the receptor in the HA-with-2-abs.wrl model, and a third antibody can printed separately from the HA-abs.wrl file. Fitting the separate antibody to the receptor demonstrates the binding groove that crosses each subunit. Mutations in the protein in the binding groove region impact the ability of antibodies to bind to the receptor, thus affecting the ability of the body's immune system to fight the infection.