Indirect immunofluorescence staining showing binding to, and internalization of, VP5 and VP2 by L929 cells. (A and C) Controls of binding and internalization in the absence of purified VP5 protein. (B) VP5 bound to cell surface at 4°C. (D) No change of staining with further incubation at 37°C for internalization. (E) The control VP2 protein, however, shows strong internalization by L929 cells. Magnification, ×3,200.