However, compared with normal synovial tissues, the synovial macrophages of patients with RA highly express matrix metalloproteinase‐12 (MMP12), TNF‐α and the transcription proteins PHD3 and CCR2 of the pro‐inflammatory gene EGLN3 and show a lower expression of the M2 macrophage indicator CD209.39 Here, MMP12 is linked to rheumatoid arthritis.