Comparison of the efficiency of fusion of envelope with sMAGI cells compared to cells expressing CCR5. Envelope-positive syncytia scored using an immunofluorescence fusion assay are shown. The viruses tested are indicated at the bottom of each chart and the coding for the cell lines tested is indicated at the very bottom of the figure. (A) Fusion of HIV-1 SF162 and a CXCR4 viral envelope, HIV-1 SF33 with sMAGI, sMAGI-CCR5, MAGI and MAGI-CCR5. (B) Fusion of SIVMneCL8 envelope with sMAGI, sMAGI-CCR5 and MAGI-CCR5. The HIV-1 envelopes shown in panel A were included as controls. Arrows indicate results where the values were above 0, but below 10 syncytia.