FIG. 4.

The HLA-gp42 interaction sites at class II β glutamic acid residue 46 and arginine 72 are necessary for EBV coreceptor activity. HLA class II expression and sgp42 binding were determined by flow cytometry by using a FacsCalibur (Becton Dickinson). Surface expression of HLA-DQ was detected by using the primary anti-HLA-DQ antibody Ia₃ conjugated to biotin, followed by the secondary streptavidin antibody conjugated to allophycocyanin (Pharmingen). sgp42 was detected by using the polyclonal antibody PB1114, followed by a goat anti-rabbit secondary antibody conjugated to fluorescein isothyocyanate (Pharmingen). Entry of EBfaV-GFP was determined by flow cytometry analysis of GFP expression. The number in the lower right quadrant is the infection rate, with DQ 2 set at 1. The number was calculated by taking the percentage of GFP-positive cells divided by the number of HLA-DQ-positive cells. n.a., not applicable as cells were not positive for HLA-DQ expression. Dot plots contain 40,000 events. These experiments were performed a minimum of three times with similar results obtained.