CD8+T cell phenotype and differentiation status. Using a whole blood staining, the phenotype and differentiation status of CD8+ T cells were determined in HC and ESRD patients not on RRT or receiving RRT. The absolute number of CD8+ T cells of young (age: <50 years) and old (age: ≥50 years) HC and these ESRD patients was dissected into a naïve (closed bars) and memory (open bars) compartment (A). Next, the composition of the memory compartment (CM in black, EM in grey and EMRA in white bars) of CD8+ T cells is given for young and old HC and ESRD patients on RRT or not (B). In addition, we also determined the percentage memory CD8+ T cells lacking CD28 (i.e. CD28null) on their cell surface as another marker for T cell differentiation for HC (grey bars) and ESRD patients not on RRT (white bars) or receiving RRT (black bars) (C). Bars represent the means + SEM and statistically significant differences between the groups are shown (one symbol: p < 0.05, two symbols: p < 0.01, three symbols: p < 0.001).