CD4 and chronic obstructive pulmonary disease: The percentage of CD4+ T lymphocytes and Treg cells in mouse lung tissue following COPD decreased compared with the control group (p < 0.01, p < 0.001), while the percentage of CD8+ T lymphocytes, MDSCs, B lymphocytes, Eos and NK cells significantly increased (p < 0.001), and the level of CD4/CD8 decreased (p < 0.05) (Figure 4).