Reduced CCR5 expression on peripheral blood– and LN-derived CD4⁺ T cells in natural hosts of SIV. (A) Representative contour plots showing CD4 and CCR5 staining of peripheral blood–derived T cells of healthy uninfected individuals belonging to 5 nonnatural/recent hosts of HIV/SIV—humans (Hu), rhesus macaques (RM), pigtail macaques (PTM), cynomolgus macaques (CYM), and baboons (Bab)—and 5 natural hosts of SIV—sooty mangabeys (SM), Caribbean African green monkeys (AGM), mandrills (MND), sun-tailed monkeys (SUN), and chimpanzees (Cy). (B) Representative contour plots showing CD4 and CCR5 staining of T cells isolated from the LNs of RMs, baboons, SM, AGM, and mandrills. (C) Summary of CCR5 expression on blood-derived CD4⁺ T cells of the primate species listed in panel A. Statistically significant differences in CCR5 expression on CD4⁺ T cells from natural and nonnatural hosts of SIV was determined by one-way nonparametric ANOVA (Kruskal-Wallis) followed by the Dunn multiple comparison test. For nonnatural human hosts of SIV versus natural AGM hosts of SIV, P < .05; for all other nonnatural hosts versus natural hosts, P < .001.