CX3CRs

CX3CR1, also known as the CX3C chemokine receptor 1, is a G protein-coupled receptor that plays a crucial role in immune cell trafficking and function. It is primarily expressed on monocytes, macrophages, natural killer cells, and T lymphocytes. The sole known ligand for CX3CR1 is the chemokine fractalkine (CX3CL1), also known as fractalkine or FDC2. Fractalkine is unique in that it exists in both a soluble form and a membrane-bound form, which is tethered to the surface of endothelial cells and epithelial cells.

The interaction between CX3CR1 and fractalkine is essential for the migration of leukocytes from the bloodstream to sites of inflammation or tissue damage. When fractalkine is presented in its membrane-bound form on activated endothelial cells, it can arrest circulating leukocytes expressing CX3CR1, allowing them to migrate into the underlying tissue. The soluble form of fractalkine acts as a chemoattractant, guiding CX3CR1-expressing cells towards areas of inflammation. This receptor-ligand system is involved in various physiological and pathological processes, including neuroinflammation, atherosclerosis, and tumor immunity. Dysregulation of the CX3CR1-fractalkine axis has been implicated in the pathogenesis of several diseases, making it a potential target for therapeutic intervention. Research continues to explore the multifaceted roles of CX3CR1 in health and disease.