CX3CL1 and obesity due to melanocortin 4 receptor deficiency: A recent study demonstrated a high resistance of females receiving a high-fat diet to obesity by maintaining the level of Cx3Cl1-Cx3Cr1 (the chemokine fractalkine receptor C-X3-C motif 1) and its highly selective Cx3Cl1 ligand, known as the Cx3Cl1–Cx3Cr1 axis [127], while male mice show a decrease in ligand and receptor expression.