CX3CL1 and metabolic syndrome: Fractalkine/CX3CL1 is a transmembrane protein that is widely expressed in immune and non-immune human cells that occurs in two distinct for metabolic syndrome: a membrane-bound form that promotes the firm adhesion of cells expressing its cognate receptor CX3CR1, and a soluble form that is generated by the proteolytic cleavage of the transmembrane form [25].