Schematic of Discoidin domain receptor 2 (DDR2) and matrix metalloproteinase (MMP) function during acute and chronic inflammation. During acute inflammation, DDR2 on the surface of neutrophils binds to collagen resulting in the secretion of MMP-8, that processes collagen into N-acetyl Pro-Gly-Pro (Ac-PGP). Ac-PGP binds surface receptors and stabilizes chemoattracant (IL-8)–mediated chemotaxis. During chronic inflammation, neutrophils produce MMP-9 that generates Ac-PGP from collagen and Ac-PGP binds to surface receptors, including CXCR1/2 receptors, leading to more MMP-9 and chronic inflammation. Professional illustration by Paulette Dennis.