FIG. 3.

Titers of AdelH retroviruses after A-RBD-mediated target cell activation. (A) A-RBD (used undiluted) was bound to XC target cells at 37°C for 30 min. Unbound A-RBD was removed by two PBS washes, and cells were incubated at 37°C to allow internalization of A-RBD–receptor complexes. At the indicated times, cells were further washed two times with PBS and infected with retroviruses carrying A or AdelH envelope glycoproteins. (B) Detection of A-RBD fragments expressed at the surface of the target cells after incubation for the indicated periods of time at 37°C. Mean values of binding expressed as percentages of the maximal fluorescence at T₀ are shown, with the background value being the fluorescence of cells before addition of A-RBD.