FIG. 4.

The effect of soluble heparin on the infectivity of FMDV. Mixtures of the indicated FMDV (50 to 300 PFU) and the amount of heparin (Sigma; from bovine lung, sodium salt) were incubated in DMEM for 10 min at 25°C. Then the mixtures were applied to confluent monolayers of either BHK-21, wild-type CHO (WT-CHO), or pgsA-745 CHO cells. After an adsorption period of 1 h at 37°C, the monolayers were washed and overlaid with DMEM containing 1% fetal calf serum and 0.5% agar. Plaques were visualized by staining with crystal violet. Plaque formation by mutant p100RGG required the presence of DEAE-dextran (0.08 mg/ml) in the semisolid medium. Percent plaque reduction was calculated relative to parallel assays with each virus and cell type in the absence of heparin. In addition, virulence assays were performed, as described in Materials and Methods, in the absence or presence of heparin (1 mg/ml) in the virus to be tested. Virulence values are given in parentheses (absence or presence of heparin) and are defined as indicated in Materials and Methods. Some viruses were tested only in BHK-21 cells because they do not infect CHO cells under the assay conditions used (see the text and Table 3).