FIG. 3.

Expression of the α4 integrin subunit enhances Py infectivity in the α4-negative BALB/c 3T3 fibroblasts. (A) Flow cytometric analysis of α4 and β1 subunit surface expression on mock-transfected and α4-BALB/c 3T3 (α4+) cells. Cells were either preincubated (heavy line) or not preincubated with anti-α4 or anti-β1 Abs for 30 min on ice as described in Materials and Methods. After washes, the cells were incubated with PE-conjugated secondary Abs. The histograms display relative cell numbers as a function of relative fluorescence intensities. (B) The α4-expressing BALB/c 3T3 cell line is more susceptible to Py infection than the mock-transfected clone. Mock-transfected and α4-BALB/c 3T3 cells were either pretreated or not pretreated for 1 h at room temperature with 30 μg of anti-α4 or its isotype Ab per ml before infection with Py for 1 h at 37°C. After the 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 reported with the value obtained when mock-transfected cells were preincubated with DMEM without competitors (control) considered to be 100% virus infectivity (corresponding to an average of 3% LT positive cells). Data correspond to the means and standard deviations from two independent experiments.