['To investigate the relationships between B, T lymphocyte attenuator (BTLA), regulatory T (Treg) cells and reduced lung function of patients with rheumatism.', "The lung function of 482 patients of rheumatism, including rheumatoid arthritis (RA, 198 cases), ankylosing spondylitis (AS, 114 cases), Sjogren's syndrome (SS, 102 cases) and osteoarthritis (OA, 68 cases), were detected by spirometer. BTLA and Treg cells of peripheral blood in 482 patients with rheumatic diseases were observed using flow cytometry.", 'Lung function and the expressions of BTLA and Treg cells were lower in patients with rheumatism than those in normal controls. Lung function parameters, such as forced expiratory volume in 1 second (FEV1), peak expiratory flow (PEF), forced expiratory flow at 50% of forced vital capacity (FEF50), forced expiratory flow at 75% of forced vital capacity (FEF75), were higher in the rheumatism group with normal BTLA and Treg cells than those in the group with abnormal BTLA and Treg cells (P<0.05 or P<0.01). Correlation analysis showed that there were positive correlations between lung function parameters orced vital capacity(FVC), maximal voluntary ventilation (MVV), FEV1, forced expiratory flow at 25% of forced vital capacity (FEF25), FEF50 and BTLA, Tregs. There were negative correlations between lung function parameters FVC, FEV1, FEF50, FEF75 and IL-4, IgA, IgM (P<0.05 or P<0.01).'] Is [ The decline in lung function associated with a decrease in the number of BTLA⁺ lymphocytes and regulatory T cells in patients with rheumatism ]?