Table 2. Fusion host range of the HERV-FRD envelope.

		Fusion index*
Species	Target cells	HERV-FRD	HERV-W	A-Rless	None
Mouse	NIH3T3	1.0 ± 0.9	0.2 ± 0.5	41 ± 17	0.4 ± 0.3
Hamster	CHO	1.8 ± 0.6	1.3 ± 0.8	1.8 ± 0.4	1.0 ± 0.5
Cat	G355—5	90 ± 2	2.2 ± 3.2	83 ± 3	0.7 ± 0.8
Monkey	Cos-7	20 ± 4	62 ± 3	19 ± 4	13 ± 3
Human	TE671	66 ± 6	56 ± 10	39 ± 8	3.1 ± 1.8
	293T	81 ± 7	90 ± 4	9 ± 3	0.3 ± 0.6
	HeLa	1.8 ± 0.7	65 ± 9	23 ± 6	1.0 ± 0.4

^*Target cells were transfected with expression vectors for the HERV-FRD envelope, the HERV-W envelope, the hyperfusogenic mutant amphotropic MLV envelope (A-Rless), or no protein (none) as a negative control, and fusion indices were determined as indicated in Materials and Methods (means ± SDs; n = 5)