CD4⁺ T cells exhibit a senescent profile in ICL. (A and B) Flow-cytometric analyses of CD27, CD28, CD57, and KLRG1 expression in CD3⁺CD4⁺-gated PBMCs from healthy, elderly, SARC, and ICL subjects. Quadrants were set on controls stained with the corresponding isotype control Ab. Representative dot plots showing coexpression of CD27 and CD28 or CD57 and KLRG1 are shown (A). Comparison of the frequencies of CD27⁻, CD28⁻, HLADR⁻, CD57⁻, KLRG1⁻, and granzyme B-expressing CD4⁺ T cells in healthy (n = 28), elderly (n = 6), SARC (n = 8), and ICL (n = 20) individuals. Lines indicate the mean ± SD values, and each symbol represents the value from an individual (B). (C and D) Telomerase activity (C) and telomere length (D) were measured in PBMCs from the aforementioned groups by Telomere Repeat Amplification Protocol, followed by enzyme-linked immunosorbent assay detection and quantitative PCR, respectively. Results (mean ± SD) are from 3 independent experiments and show the optical density values (C) or are expressed as the ratio of telomere repeat copy number (T) to albumin copy number (a single-copy gene, S) within the same DNA sample in each group (D). Kruskal-Wallis H test values and associated P values are indicated. *P < 0.05, **P < 0.005, and ***P < 0.0005 compared with healthy leukocytes (as determined using the Mann-Whitney U test).