FIG. 2.

Integrin ligands and function-blocking Abs reduce Py infectivity. (A and B) Py infectivity is inhibited by integrin ligands in a dose-dependent manner. Swiss 3T3 cells were pretreated for 1 h at room temperature with various concentrations of integrin specific ligands, i.e., fibronectin (Fn), vitronectin (Vn), collagen (Cl), or tenascin (Tn) (A) or α-chymotryptic fibronectin fragments (Fn40 or Fn120) (B), before infection with virus particles for 1 h at 4°C. The virus inoculum was removed, and cells were further incubated for 20 h at 37°C before fixation. Infected cells were immunostained for LT (see Materials and Methods). Results are presented as the percentage of virus infectivity obtained when cells were preincubated with DMEM without competitors (control). One hundred percent of virus infectivity corresponded to an average of 7 to 10% LT positive cells. Data correspond to the means and standard deviations from two or three independent experiments, each performed in duplicate or triplicate. (C) Inhibition of Py infectivity by integrin-specific Abs. Swiss 3T3 cells were pretreated for 1 h at room temperature with a 30-μg/ml concentration of Abs to specific integrins before infection with Py for 1 h. After virus particles were removed, cells were further incubated for 20 h at 37°C before fixation. Infected cells were stained for LT by indirect immunofluorescence. Results are presented as described for panels A and B. Data correspond to the means and standard deviations from two or three independent experiments, each performed in duplicate or triplicate.