CD4 and idiopathic pulmonary fibrosis: There was a markedly 2.5-fold greater proportion of CD4+ cells in COPD and IPF lung tissues than in healthy lung tissue from donors (p ≤ 0.006; median [range]: 33.5% [27.0–50.5], 30.9 [20.1–38.0] and 13.5% [4.3–33.7], respectively) (Table 2, Figure 2B).