Chlamydia pneumoniae (C. pneumoniae) is a common respiratory pathogen associated with many inflammatory diseases. There are few data concerning the lymphocyte subsets in middle-aged and elderly individuals with C. pneumoniae infection. A total of 191 patients were included in this study. The study population was categorized into the middle-aged group (40–64 years old) and the elderly group (65–89 years old). Lymphocyte subsets in peripheral blood were examined with multi-colored flow cytometry. Immunological monitoring included lymphocyte subsets, C. pneumoniae IgG and IgM serology. In the middle-aged group, 69.83% individuals presented IgG positivity, which was associated with the inverted CD4/CD8 ratio. Individuals with C. pneumoniae IgG positivity also presented an increased percentage of CD8⁺CD28⁻ cells and a decreased CD4/CD8 ratio when compared to weakly-positive individuals. In the elderly group, C. pneumoniae IgG positivity was associated with a significant increase in the percentage of CD3⁺CD56⁺CD45⁺ (NKT) cells. In conclusion, altered lymphocyte homeostasis was shown in middle-aged individuals with C. pneumoniae IgG positivity. The senescent phenotypes of T cells might be associated with C. pneumoniae infection in middle-aged individuals.

肺炎衣原体（C. pneumoniae）是一种常见的呼吸道病原体，与许多炎性疾病有关。关于中老年人肺炎衣原体感染的淋巴细胞亚群的数据很少。本研究共纳入191名患者。研究人群分为中年组（40-64岁）和老年组（65-89岁）。用彩色流式细胞仪检查外周血中的淋巴细胞亚群。免疫学监测包括淋巴细胞亚群，肺炎衣原体IgG和IgM血清学。在中年组中，有69.83％的人表现出IgG阳性，这与CD4 / CD8比率倒置有关。肺炎衣原体个体IgG的阳性也呈现CD8的增加的百分比⁺ CD28 ^- 细胞，并且当相比较弱阳性个体降低CD4 / CD8比率。在老年组中，肺炎衣原体IgG阳性与CD3 ⁺ CD56 ⁺ CD45 ⁺（NKT）细胞百分比的显着增加有关。总之，在肺炎衣原体IgG阳性的中年人中显示出淋巴细胞稳态的改变。T细胞的衰老表型可能与中年人的肺炎衣原体感染有关。