CD4 and asbestosis: Here, we assessed the correlations between PD-1 expression and pulmonary function parameters and found that the proportions of PD-1+ CD4+ T cells (r = 0.591, P = 0.008) and PD-1+CD8+ T cells (r = 0.507, P = 0.027) were positively correlated with the percentage of FVC predicted in the asbestosis group (Fig. 7a, b).