Figure 2. Receptor mediated resistance to SIVcpz entry is a trait acquired in gorillas and chimpanzees.

(A) Cladogram of ape species, highlighting the nodes for which ancestral CD4 sequences were reconstructed. The virion diagram next to some ape species represents apes that are infected by SIV/HIV. (B) An amino acid alignment of the CD4 D1 domain of human, chimpanzee, gorilla, and the inferred ancestral CD4 sequences. Dots represent identical residues compared to human and distinct amino acids and numerical positions are noted. Bolded residues on the human sequence represent sites known to directly interact with HIV-1 Envelope (Liu et al., 2017). (C) Cladogram of HIV-1 and SIVcpz based on previously published work (Takehisa et al., 2007), highlighting genetic relationships of the envelope (Env) clones used in this study. (D, E) HIV-1ΔEnv-GFP viruses were pseudotyped with Envs (top of graphs) from diverse (D) SIVcpz or (E) HIV-1 strains. Cf2Th cells stably expressing human CCR5 and various CD4s (X-axis) were infected with various volumes of these pseudoviruses and then analyzed by flow cytometry 48 hours post-infection. GFP positive cells were enumerated within the CD4/CCR5 positive gate and virus titers (transducing units per milliliter; TDU/mL) were determined for those samples falling within the linear infection range (n = 2 titration points). The mean virus titers obtained from each of three independent experiments were plotted (dots), with error bars representing the standard error of the mean (SEM). Dotted lines represent the lower limit of detection for this assay. SIVcpz-Ptt and SIVcpz-Pts refer to SIVs derived from the chimpanzee subspecies Pan troglodytes troglodytes or Pan troglodytes schweinfurthii, respectively.