Frequency of CD4⁺ CD45R0⁺ memory cells and of CD4⁺ CD45R0⁺ memory cells coexpressing BLR1 in healthy and HIV-infected subjects. Peripheral blood lymphocytes (PBL) were stained with CD4-FITC, CD45R0-PE, and BLR1-biotin/streptavidin-cychrome as described in the Materials and Methods. Gates were either set at CD4⁺ cells to determine the percentage of T-helper cells associated with the CD45R0 isoform (○) or at CD4⁺ CD45R0⁺ cells to determine the percentage of T-helper memory cells coexpressing BLR1 (•). Results are the mean ± SD. *P < .05, **P < .01, and ***P < .001, always versus HIV⁻ control (Mann-Whitney test).