Effects of receptor expression levels on virus infection.

Serial dilutions (1 μg to 0.009 μg per 12 wells) of STRL33 and CCR5 expression plasmids were transiently transfected into 293T cells along with a constant amount of 1 μg CD4. Two days later, cells were harvested with Versene and stained for either CCR5 (mAb 2D7) or STRL33 (mAb 699). CCR5 and STRL33 levels on gated GFP⁺ cells (ie, infected cells) were quantified using QFACs as described. The relative percentage (%) of GFP⁺ cells was linearly regressed against CCR5 or STRL33 levels (presented as the number of ABS). Data from 1 representative experiment out of 3 experiments with SIVmac316 and SIVmacBK28 env protein–pseudotyped reporter viruses are presented. The linear trend for the CCR5 infections can be extrapolated back to approximately 400 ABS as previously shown.31