CD4 and silicosis: Due to the negative correlation between PD-1 and IFN-γ and there is no study on T cell exhaustion in silicosis patients before, this study analysed the expression of PD-1 in silicosis and found that the peripheral blood lymphocytes of patients with silicosis highly expressed PD-1, and the PD-1 highly expression can inhibited the secretion of IFN-γ by lymphocytes (especially CD4+T cells).