FIG. 2.
Use of chemokine receptors in a cell fusion assay. (a) The abilities of the HIV-1DH12 (vvDHenv), HIV-1AD8 (vvADenv), HIV-1IIIB (BH8 clone, vSC60 [5]), HIV-1JR-FL (vCB28 [5]), and HIV-189.6 (vBD3 [18]) envelope glycoproteins to mediate fusion with quail QT6 cells expressing CD4 and the indicated coreceptors were determined by a gene reporter fusion assay. The extent of fusion was expressed (as signal-to-noise ratio) relative to background levels (i.e., the spontaneous fusion seen with QT6 cells expressing CD4 and CXCR2). (b) Fusion of the chimeric envelope proteins (expressed by transfecting pNVVDH120A to -I) with cells expressing CCR5 or CXCR4 in conjunction with CD4 was determined. The results were averaged for three experiments, each of which gave identical patterns of coreceptor usage for each envelope protein. Absolute numbers varied between experiments due to differences in cell numbers and transfection efficiencies in independent experiments. It also should be noted that the time elapsing between the addition of the substrate and the determination of luciferase activity strongly influences the absolute light units obtained, though not the pattern of coreceptor use. The variable regions of HIV-1DH12 gp120 transferred into the chimeric envelope are indicated at the top.