Table 1.

Effect of three different soluble RBDs on MLV (env ΔRBD) infection (units/ml × 10⁴ +/− SE)

Virus	Soluble RBD (100 nM)
	A-RBD	Fr-RBD	X-RBD
A-MLV (env ΔRBD)	0	1.17  (±0.11)	0
Fr-MLV (env ΔRBD)	0	1.39  (±0.19)	0
X-MLV (env ΔRBD)	0	1.09  (±0.12)	0

Human 293 mCAT1 cells were challenged with A-, Fr-, or X-MLV (env ΔRBD) encoding lacZ in the absence or in the presence of soluble A-, Fr-, or X-RBD (100 nM). Two days later, cells were fixed and lacZ+ cells were counted. Data are presented as infectious units/ml (×10⁴) with one standard error indicated. No lacZ+ cells were observed in the absence of soluble RBD.