FIG. 6.

Binding of chicken and quail sTva-mIgG to wild-type and mutant ALV(A) glycoproteins. Uninfected DF-1 cells and DF-1 cells infected with wild-type RCASBP(A)AP virus (A) or the E149K (B), Y142N (C), or Y142N/E149K (D) mutant viruses (Fig. 4) were fixed with paraformaldehyde, incubated with different amounts of the chicken (○) or quail (■) sTva-mIgG protein, and the envelope glyco- protein–sTva-mIgG complexes were bound to goat anti-mouse Ig antibody linked to phycoerythrin. The levels of phycoerythrin bound to the cells were measured by FACS, and the maximum fluorescence was estimated (see Materials and Methods). The data were plotted as percent maximum fluorescence bound against sTva-mIgG concentration. The values shown are an average of four different experiments. Error bars show standard error.