FIG. 2.

R18-labeled IBV virions retain infectivity in BHK cells and show no loss of S1. To determine relative infectivity, purified IBV strain Beaudette was incubated with or without R18. The protein concentration of each virus preparation was assayed via Bio-Rad protein assay, and virus infectivity was assessed by infecting BHK cells using immunofluorescence microscopy (A). To determine virus integrity, 500 ng of either R18-labeled or unlabeled IBV strain Beaudette was use to coat an ELISA plate, and the S1/S2 ratio of each sample was determined via anti-S1 (15:88) and anti-S2 (9:4) monoclonal antibody staining, followed by anti-mouse horseradish peroxidase labeling and ABTS development (B). The error bars represent the standard errors of the mean.