CXCL1 and infection: Indeed, in vivo, a complex network of soluble (e.g., chemokine gradients) and solid (e.g., ECM proteins, epithelial cells) cues guides maturation and migration of neutrophils from the BM to sites of infection, with the chemokines CXCL1 and CXCL2 being the most potent neutrophil attractants in vivo [43, 44].