MMP12 and rheumatoid arthritis: Macrophages are the most abundant immune cells found in RA synovium, where they produce the predominant pro-inflammatory cytokines involved in RA pathogenesis (TNFα, IL-1β, and IL-6), with chemoattractant factors (CCL2 and IL-8) and metalloproteinases (MMP-3 and MMP-12) [99,100].