Age-associated changes in major lymphocyte subsets and sex-specific patterns in healthy Chinese adults

To delineate age-associated changes in major lymphocyte subsets in healthy Chinese adults, identify key inflection points, and explore sex-specific patterns. Flow cytometry data of peripheral blood T, B, and NK cell subsets were collected from 6,550 healthy individuals aged 18–96 years at Hubei Provincial People’s Hospital. Piecewise regression models were used to identify inflection points where the rate of change in immune parameters accelerates. A composite immune index (CII) was constructed via principal component analysis (PCA). Immune characteristics were compared across four age groups (youth, young middle-aged, middle-aged elderly, elderly) and between sexes. Key inflection points were identified: CD8 + T cell percentage and CD4+/CD8 + ratio declined significantly around age 54, while CD4 + T cell and B cell counts showed accelerated decline after ages 63.12 and 62.00, respectively. Total T cell count declined most rapidly after age 67.50; The CII, integrating 11 immune parameters, exhibited a significant inflection point at age 63 (p < 0.001), with the rate of decline accelerating from − 2.64 units/year to − 10.66 units/year thereafter; In individuals aged ≥ 63 years, females maintained higher CD4 + T cell counts and percentages, B cell counts and percentages, CD4+/CD8 + ratio, and total T cell percentage, whereas males had higher NK cell counts and percentages. This study delineates the age-associated trajectories of lymphocyte subsets in healthy Chinese adults, identifying age 63 as a data‑driven inflection point associated with accelerated adaptive immune decline. Pronounced sexual dimorphism in late-life immune profiles underscores the need for sex-specific strategies in immune health assessment and personalized health management.