Table 2.

Fusion activity of HERV-W Env in receptor-blocked TE671 cells

Type of assayRetrovirusa or glycoproteinbResultsc,d for receptor-blocked target cellse
NonePiT-2PiT-1RDR
Virus-cell fusionMLV-Aa,c 107 5 × 102 107 107
GALVa,c 106 106 5 × 101 106
RD114a,c 107 107 107 2 × 102
Controla,c,f <1<1<1<1
Cell-cell fusionA-Rlessb,d 43.4 0.834.147.6
HERV-Wb,d 79.074.577.15 0.48
Controlb,d  0.1 0.4 0.2 0.3
  • a Retrovirus from which Env was derived.

  • b Fusogenic envelope glycoprotein.

  • c Titers (as lacZ i.u. per milliliter) of lacZ retrovirus vectors pseudotyped with the indicated envelope glycoproteins were determined on the receptor-blocked target cells. These pseudotyped lacZvectors were harvested from the supernatants of TELCeB6 cells stably transfected with expression plasmids encoding the envelope glycoproteins derived from the indicated retroviruses.

  • d Fusion indices (as percentages) determined after transfection of the indicated fusogenic envelope glycoproteins by using the receptor-blocked TE671 cells as target cells. The background value of syncytium formation was provided by transfecting a plasmid expressing the HERV-W env gene in the antisense orientation (control).

  • e The target cells were TE671 subclones stably expressing the envelope glycoproteins derived from the MLV-A, GALV, and RD114 retroviruses that respectively recognize the PiT-2, PiT-1, and RDR receptors, thus blocking the accessibility of exogenously presented retroviral envelopes to these receptors.

  • f Control, no Env expression plasmid was transfected into TELCeB6 cells.