Expression of cell surface molecules. (A) The pE T-cell subset shares cell surface molecules with effector T lymphocytes. Purified CD8 T cells were stained with CD8, CCR7, CD45RA, CD27 mAbs and other mAbs as indicated. Histograms show the proportion of positive cells among RA⁺CCR7⁺27⁺ (N), RA⁺CCR7^–27⁺ (pE), and RA⁺CCR7^–27^– (E) gated subsets. These results were consistent in 8 healthy individuals. Note that our experimental procedure (see “Materials and methods” for details) to analyze N, pE, and E CD8 T subpopulations allows the exclusion of any residual contaminating NK cells as shown by anti-CD3 costaining. (B) Analysis of CD28 expression on N, pE, and E CD8⁺ T-cell subsets. Naive and effector T cells displayed, respectively, RA⁺CCR7⁺27⁺28⁺ and RA⁺CCR7^–27^–28^– phenotypes. In contrast, the pE CD8 subset contained CD28⁺ as well as CD28^– cells. Accordingly, pE T cells are split into pE₁ (RA⁺CCR7^–27⁺28⁺) and pE₂ (RA⁺CCR7^–27⁺28^–) subsets.