Chemokine receptor expression on CD8 T-cell subsets. (A) Protein and mRNA levels of chemokine receptors were assessed on naive, central memory (CM), effector memory (EM), and CD45RA re-expressing effector memory (EMRA) CD8 T cells. CXCR1 and CX3CR1 were selectively expressed on EMRA CD8 T cells, while CCR4 was selectively expressed on CM and EM CD8 T-cell subsets. Note the generally tight association of protein expression and mRNA levels. (B) Representative examples of cell surface expression of CXCR1 and CCR4 on naive, CM, EM, and EMRA CD8 T cells. (C) Distribution of CXCR1⁺ CD8 T cells among subsets of CD8 T cells defined by expression/absence of CD27 and CD28. CXCR1⁺ CD8 T cells were highly enriched within the CD27^– and CD28^– subpopulations of CD8 T cells. Data represent the mean (± SD) of 3 to 12 healthy blood donors. Several donors were tested more than once. n.d. indicates not done.