OBJECTIVE To explore the differences in T lymphocyte subsets of the severe pneumonia (SP) patients among different age groups and analyze its relationship with the prognosis.

METHODS A total of 100 patients with SP who were treated in the First Affiliated Hospital of Zhengzhou University from Mar. 2018 to Jun. 2024 were enrolled in the study and were divided into the youth group with 22 cases (less than 40 years old), the middle age group with 36 cases (aging between 40 and 65 years old) and the old age group with 42 cases (more than 65 years old). The clinical data and the laboratory test indexes were compared among the three groups. The levels of CD₃⁺, CD₄⁺, CD₈⁺ and CD₄⁺/CD₈⁺ before and after the treatment were compared among the three groups by repeated measures variance method.

RESULTS The length of hospital stay of the old age group was longer than those of other two groups; the acute physiology and chronic health evaluation (APACHE)Ⅱ score, clinical pulmonary infection score (CPIS) and the levels of interleukin-6 (IL-6), platelets (PLT), white blood cells (WBC), C-reactive protein (CRP) and lactic dehydrogenase (LDH) levels were higher in the old age group than in other two groups (P < 0.05). The levels of CD₃⁺, CD₄⁺, CD₈⁺ and CD₄⁺/CD₈⁺ of all the three groups were elevated after the treatment, with the highest in the young group after the treatment for 2 months the CD₃⁺ level(56.25±5.21)%, the CD₄⁺ level(35.65±2.43)%, the CD₈⁺ level(22.33±1.74)%, and the CD₄⁺/CD₈⁺ (1.97±0.25), the lowest in the old age group after the treatment for 2 months the CD₃⁺ level (49.46±2.67)%, the CD₄⁺ level(28.45±3.45)%, the CD₈⁺ level (15.68±2.23)%, and the CD₄⁺/CD₈⁺(1.46±0.14), there were significant differences (F=21.830, P=0.045;F=41.870, P=0.024;F=71.914, P=0.014;F=48.463, P=0.020).

CONCLUSION The CD₃⁺, CD₄⁺, CD₈⁺ and CD₄⁺/CD₈⁺ have great clinical significance in diagnosis of SP for different age groups of patients and assessment of illness condition.