CXCL12 and rheumatoid arthritis: And specially, the ErbB receptor, EGFR, was highly expressed by HBEGF− fibroblasts, which also highly expressed MDK (Midkine) [43], and CXCL12 (C-X-C Motif Chemokine Ligand 12) [44, 45] that engage in the pathophysiology of RA.