In addition, the mean CD4+ T cells counts in the CTD-ILD group was markedly lower than that in the IPF group and the healthy control group(0.44±0.25×109/L, 0.79±0.29×109/L and 0.88±0.33×109/L, respectively, P<0.05). Here, CD4 is linked to idiopathic pulmonary fibrosis.