Abstract: OBJECTIVE To explore the risk factors for pulmonary infection and the changes of peripheral blood CD4/CD8 cell ratio, percentages of B cells and NK cells in patients with rheumatoid arthritis. METHODS Total of 120 patients with rheumatoid arthritis in the Infectious Immunology Department of Tianjin Fifth Central Hospital from Mar 2018 to Jan 2020 were enrolled. The patients were divided into the infection group（n=29） and non-infection group（n=91） according to whether they got pulmonary infection. The distribution of pathogens were investigated, general patient information was collected through electronic medical records, the nutrition control status score（CONUT） and prognostic nutrition index score（PNI） were calculated, and the risk factors for pulmonary infection in RA patients were evaluated. The CD₄⁺/CD₈⁺ ratio, B cells and NK cells in the peripheral blood of the objects were detected by flow cytometry, and the severity of infection was graded using the lung infection score. RESULTS Twenty-nine strains of pathogens were isolated from 29 infected patients, including 16 strains of gram-negative bacteria, accounting for 55.17%, 5 strains of fungi, accounting for 17.24%, and 8 strains of gram-positive bacteria, accounting for 27.59%. Pseudomonas aeruginosa, Candida albicans and Staphylococcus aureus were the strains with higher detection rate. Logistic regression analysis showed that the course of disease ＞10 years, smoking, active RA, CONUT score ≥2 points, PNI score ＜45 points are risk factors for pulmonary infection in RA patients（P＜0.05）. CD₄⁺/CD₈⁺ ratio in the infected group was significantly lower than that in the non-infected group; B cells and NK cells were significantly higher than that in the non-infected group（P＜0.05）. With the increase of infection degree, the level of CD₄⁺/CD₈⁺ continued to decrease, the level of B cells and NK cells continued to increase, and the overall difference was significant（P＜0.05）. CONCLUSION Disease course ＞10 years, smoking, active RA, CONUT score ≥2 points, PNI score ＜45 points are risk factors, which should be monitored, for pulmonary infections in RA patients. Dysregulation of CD₄⁺ T cells, B cells and NK cells are involved in pulmonary infections, and the mechanism should be further studied.