PTPRC and silicosis: We found that the expression of RAB20 genes is markedly decreased in monocytes and macrophages from silicosis patients, while the RAB20 gene expression in T cells (CD3+), CD4+ T cells (CD3+ and CD4+), CD8+ T cells (CD3+ and CD8+), monocytes (CD14+), macrophages (CD68+), B cells (B220+), and hemopoietic stem cells (HSCs, CD34+) from silicosis patients was not altered (Figure 1A).