Decreased susceptibility of P₁^k PBMCs to R5 and X4 HIV-1 infection inversely correlates with P^k and does not correlate with CD4 and/or chemokine coreceptor expression. (A) PHA-activated PBMCs were infected with HIV-1_Ba-L (0.5 ng HIV p24^gag/5 × 10⁵ cells) and (B) PHA/IL-2–activated PBMCs were infected with HIV-1_IIIB (MOI, 0.3). Viral propagation was monitored by p24^gag antigen up to 12 days and plotted as a function of time: (A) **P < .002. (B) *P < .05. Data are representative of the mean plus or minus SEM, where n = 4 infection data points. (C-F) Scatter plots of PBMCs labeled with anti–CD4 PerCP Cy5.5, anti–CCR5 GAM-FITC (or GAM-APC), and anti–CXCR4-PE were analyzed, and background compensated to isotype controls. Alternatively, anti–CD4 PerCP Cy5.5 and anti-P^k GAM-APC were used to label PBMCs and analyzed as described. (C) Percentage of cell populations expressing CD4, CCR5, and CXCR4, present in PHA-activated (left) or PHA/IL-2 activated PBMCs (right) plotted as histograms for ease of comparison. (D) MFI of surface expressed CD4, CCR5, and CXCR4 was measured on ungated cell populations and fold difference in expression levels calculated based on control MFI values for PHA-activated PBMCs (left) or PHA/IL-2–activated PBMCs (right). (E) Percentage of P₁^k-PBMC cell populations expressing surface P^k (left) and P^k expression levels based on MFI (right) are represented as fold difference based on control values. (F) Scatter plots representing CD4 and P^k expressing cell populations. (Top panel) PHA-activated PBMCs. (Bottom panel) PHA/IL-2-activated PBMCs. Left: Control PBMCs. Right: P₁^k PBMCs. ◇ or □ represent healthy PBMCs controls designated C-a or C-b (Table 3); (■), P₁^k = P₁^k PBMCs designated P₁^k-a or P₁^k-b (Table 2).