Reduced CCR5 expression on monocytes in natural hosts of SIV. (A) Representative contour plots showing CCR5 expression on monocytes in healthy uninfected individuals belonging to progressing (RMs and PTMs) and nonprogressing (SMs and AGMs) NHPs. (B) Summary of CCR5 expression on monocytes of the primate species listed in panel A. One-way nonparametric ANOVA (Kruskal-Wallis) followed by the Dunn multiple comparison test and the Mann-Whitney U test. For nonnatural RM hosts of SIV versus natural SM and AGM hosts, P > .05; for nonnatural PTM hosts of SIV versus natural SM and AGM hosts, P < .001.