It has been reported that the SDF-1/CXCR4 axis is constitutively expressed in a wide range of tissues such as the brain, heart, kidney, liver, lung, and spleen and also involved in several diseases such as rheumatoid arthritis, ischemic cardiomyopathy, and several brain diseases [35–37]. Here, CXCL12 is linked to rheumatoid arthritis.