CD4 and CD8⁺ T-cell homeostasis at different ages and CD45RA and CD27 expression within CD4 and CD8 T cells in patients and controls. (A-B) CD4 and CD8 T cells are lower in patients at all ages than in controls but have a slower rate of decline than controls. The gray boxes indicate the normal age-related ranges for absolute T-cell counts. (C-F) The decline of naïve CD45RA⁺CD27⁺ and the accumulation of memory CD45RA⁻CD27⁺ T cells within the CD4 and CD8 populations (expressed as a percent of the CD4 and CD8 populations, respectively) is greatly accelerated in patients compared with controls.