Abstract Background: Central nervous system tuberculosis (CNS-TB) remains a critical clinical challenge with high mortality, and its underlying immunopathological mechanisms have not been fully elucidated. This study aimed to investigate age-dependent variations in T lymphocyte subsets among CNS-TB patients and their clinical implications. Methods: In this retrospective study, we analysed 862 patients with extrapulmonary tuberculosis (EPTB) admitted to Fuzhou Pulmonary Hospital between April 2018 and April 2024. The cohort comprised 177 CNS-TB patientsand a control group of685 non-centralnervous system extrapulmonary tuberculosis (non-CNS EPTB) patients. We comprehensively compared demographic characteristics, medical history, nutritional parameters, T lymphocyte subsets (CD3+, CD4+, CD8+, and CD45+), and neutrophil-to-lymphocyte ratio (NLR) between groups, with detailed age stratification and correlation analyses. Results: Baseline characteristics, medical history, and nutritional parameters were not significantly different between the groups. CNS-TB patients exhibited markedly reduced T lymphocyte counts, which were most pronounced in the 25–54 year age group (CD3+: 735.5 vs 1010.0 cells/μL, PPP=0.013; and CD45+: 1109.5 vs 1448.0 cells/μL, PP=0.010), with diminishing intergroup differences. Correlation analysis revealed strongpositive correlations among T-lymphocyte subsets (r=0.52--0.96, Pr=0.52--0.71, Pr=-0.27--0.36, PConclusion: CNS-TB patients display characteristic T lymphocyte depletion and elevated NLRs, with dynamic age-dependent immune characteristics most prominent in immunocompetent adults. Lymphocyte counts can predict T-cell subset levels, whereas NLR values can predictinflammatory and immune response states. This study provides the first comprehensive demonstration of age-dependent immune characteristics in CNS-TB patients, offering a theoretical foundation for age-stratified immune monitoring strategies.
Chen et al. (Fri,) studied this question.