Age-Stratified Immune Characteristics in Central Nervous System Tuberculosis Patients: A Comparative T lymphocyte Subset Analysis within a Cohort of 862 Extrapulmonary Tuberculosis Patients

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 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--0.36, 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.