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 patients and a control group of 685 non-central nervous 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, P < 0.001; CD4(+): 389.0 vs 576.0 cells/μL, P < 0.001; CD8(+): 285.5 vs 358.0 cells/μL, P = 0.013; and CD45(+): 1109.5 vs 1448.0 cells/μL, P < 0.001). These differences persisted but attenuated in the 55–64 years age group, with no significant disparities in the 18–24 years and ≥ 65 years age groups. Age-stratified analysis revealed a progressive NLR increase, peaking in patients ≥ 65 years (7.07 vs 4.67, P = 0.010), with diminishing intergroup differences. Correlation analysis revealed strong positive correlations among T-lymphocyte subsets (r = 0.52–0.96, P < 0.001), significant positive correlations with lymphocyte counts (r = 0.52–0.71, P < 0.001) and moderate negative correlations with the NLR (r = − 0.27– -0.37, P < 0.001). CONCLUSION: 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 predict inflammatory 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. CLINICAL TRIAL NUMBER: Not applicable.