Selective use of primate CD4 receptors is not a result of the transmission bottleneck and instead is seen in many isolates of HIV-1 taken from human blood.

Cells stably expressing human CCR5 and human or primate CD4 (x-axis) were infected with Q23ΔEnv-GFP bearing (A) chronic Envelopes (Envs) [49], (B) early (newly infected; grey bars) and chronic (6 months post infection; black bars) Env pairs derived from the same patient [3,14,50,51], shown for one patient in each panel, or (C) Envs derived from maternal (chronic; black bars)/infant (newly infected; grey bars) transmission pairs [9], with one mother–baby pair shown in each panel. The percent cells infected (GFP-positive) was measured by flow cytometry and normalized to the percent infected with human CD4. Error bars represent the mean + SEM from two independent experiments, each with two to three technical replicates. Data associated with this figure can be found in the supplemental data file (S2 Data). CCR5, C-C motif chemokine receptor 5; GFP, green fluorescent protein.