Fractalkine is found commonly throughout the brain, particularly in neural cells, and its receptor is known to be present on microglial cells. It has also been found to be essential for microglial cell migration.[5] CX3CL1 is also up-regulated in thehippocampus during a brief temporal window followingspatial learning, the purpose of which may be to regulate glutamate-mediated neurotransmission tone. This indicates a possible role for the chemokine in the protective plasticity process ofsynaptic scaling.[6]
Fractalkine is a largecytokine protein of 373 amino acids that contains multiple domains and is the only known member of the CX3Cchemokine family. It is also commonly known under the names fractalkine (in humans) and neurotactin (in mice).[7][8] The polypeptide structure of CX3CL1 differs from the typical structure of other chemokines. For example, the spacing of the characteristicN-terminalcysteines differs; there are threeamino acids separating the initial pair of cysteines in CX3CL1, with none inCC chemokines and only one intervening amino acid inCXC chemokines. CX3CL1 is produced as a long protein (with 373-amino acid in humans) with an extendedmucin-like stalk and a chemokine domain on top. The mucin-like stalk permits it to bind to the surface of certain cells. However a soluble (90 kD) version of this chemokine has also been observed.
Soluble CX3CL1 potently chemoattractsT cells andmonocytes, while the cell-bound chemokine promotes strong adhesion of leukocytes to activated endothelial cells, where it is primarily expressed.[8] CX3CL1 elicits its adhesive and migratory functions by interacting with the chemokine receptorCX3CR1.[9] Its gene is located on humanchromosome 16 along with some CC chemokines known asCCL17 andCCL22.[8][10]
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Papadopoulos EJ, Fitzhugh DJ, Tkaczyk C, Gilfillan AM, Sassetti C, Metcalfe DD, et al. (Aug 2000). "Mast cells migrate, but do not degranulate, in response to fractalkine, a membrane-bound chemokine expressed constitutively in diverse cells of the skin".European Journal of Immunology.30 (8):2355–2361.doi:10.1002/1521-4141(2000)30:8<2355::AID-IMMU2355>3.0.CO;2-#.PMID10940926.S2CID196597758.
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