CXCL12 and idiopathic pulmonary fibrosis: Furthermore, these epithelial CXCR4+ cells, unlike their lymphoid counterparts, the CXCR4+CD45+ cells, also expressed CXCL12, indicating that the epithelium may be the primary site of fibrotic activity driven by mechanisms involving the CXCR4/CXCL12 axis in IPF.