With regard to regulatory CD4 and CD8 cell subsets, PCLF patients showed higher Th‐naïve, Th‐effector, Tc‐naïve, and Tc‐reg percentages than IPF patients (p < 0.001; p = 0.018; p = 0.005; p = 0.017, respectively). Here, CD4 is linked to idiopathic pulmonary fibrosis.