High monocyte turnover predicts AIDS progression in SIV-infected rhesus macaques. (A) Kinetics of plasma viral load (left) in 4 SIV-infected rhesus macaques at multiple time points after SIV infection. The percentages of BrdU-labeled monocytes (middle) and CD3⁺ T lymphocytes (right) at indicated time points from the same 4 SIV-infected animals are shown. BrdU staining of peripheral blood was performed at 24 hours after BrdU injection at indicated time points. †Death of the animal. In parentheses is indicated the date the animal died after the last BrdU injection experiment (182 days after infection). (B) Correlation of BrdU⁺CD8⁺ T cells with other BrdU-labeled cells in infected monkeys. Note that the turnover of monocytes is not correlated with that of other cell types examined. (C) Relation between the percentage of BrdU-labeled cells and plasma viral loads in chronically SIV- or SHIV-infected rhesus macaques. Peripheral bloods were obtained from 21 infected macaques at 24 hours after BrdU inoculation and stained for BrdU. Dots represent individual animals. The Spearman rank test was used to determine the correlation between the percentage of BrdU⁺ cells and viral loads. (D) Correlation between the survival time after the in vivo BrdU experiment and the percentage of BrdU⁺ cells, CD4 counts, and plasma viral load at the time of the BrdU injection experiment. The only parameter that predicted progression to AIDS with statistical significance was high monocyte turnover. The Spearman rank correlation test was used to determine correlations and P values. The regression line and the 95% confidence intervals are shown with continuous and broken lines, respectively (applied only for panel B).