In addition to CC chemokines and their receptors, the CX3CL1-CX3CR1 axis is also an important pathway mediating monocyte migration, playing a major, but environment-specific, role in either pro-inflammatory or pro-resolving responses [52], and contributing to the development of inflammatory diseases, such as kidney ischemia–reperfusion injury [53] and pulmonary fibrosis [50]. Here, CX3CL1 is linked to pulmonary fibrosis.