Inhibition by PVP-I of influenza virus hemadsorption activity on guinea pig erythrocytes. (A) Quantification of minimum fetuin (left panel) or PVP-I (right panel) concentration required for inhibition of virus erythrocyte agglutination. (B) Visualization of virus erythrocyte agglutination under a light microscope. Bars = 50 μm. Agglutination morphology was compared with positive (no PVP-I) and negative (no virus) controls.