Chemokine that acts as a ligand for both CX3CR1 and integrins ITGAV:ITGB3 and ITGA4:ITGB1. The CX3CR1-CX3CL1 signaling exerts distinct functions in different tissue compartments, such as immune response, inflammation, cell adhesion and chemotaxis. Regulates leukocyte adhesion and migration processes at the endothelium. Can activate integrins in both a CX3CR1-dependent and CX3CR1-independent manner. In the presence of CX3CR1, activates integrins by binding to the classical ligand-binding site (site 1) in integrins. In the absence of CX3CR1, binds to a second site (site 2) in integrins which is distinct from site 1 and enhances the binding of other integrin ligands to site 1. The soluble form is chemotactic for T-cells and monocytes, but not for neutrophils. The membrane-bound form promotes adhesion of those leukocytes to endothelial cells. Monomer. Forms a ternary complex with CX3CR1 and ITGAV:ITGB3 or ITGA4:ITGB1. Highest levels in brain (neurons). Significant levels in kidney, heart, lung and adrenal gland. A soluble short form may be released by proteolytic cleavage from the long membrane-anchored form. Belongs to the intercrine delta family.