A cytokine that is a member of the interleukin-8 superfamily of cytokines. RANTES is a protein. It is a selective attractant for memory T lymphocytes and monocytes. It binds to CCR5, a coreceptor of HIV. RANTES is an acronym for Regulated on Activation, Normal T Expressed and Secreted. It is also known as CCL5.
Fractalkine (FKN), the sole member of the CX3C chemokine family, is named for its fractal geometry.
The CX3C motif, with three amino acids between the two terminal cysteines, makes fractalkine distinct from other chemokines.
The structure of fractalkine, a membrane-bound glycoprotein with the chemokines domain atop an extended mucin-like stalk, is unique. Membrane-bound FKN can be markedly brought on primary endothelial cells by inflammatory cytokines; this form promotes the robust adhesion of monocytes and T lymphocytes.
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Soluble FKN can be released by proteolysis at an efficient chemotactic activity level for monocytes and T cells. Thus, FKN is a versatile molecule regulating both cell-cell interactions in its membrane-bound form and directed- cell migration in its soluble form.
The receptor of FKN, CXC3R1, is a G protein- couple protein, which expresses T lymphocytes, monocytes, natural killer (NK) cells, microglia, and neurons. Sulfation of tyrosine enhances the function of CX3CR1 in cell capture and firm adhesion.
Fractalkine is expressed constitutively in the kidney, heart, lung, and brain. Fractalkine has demonstrated an important role in CNS inflammation, cardiac allograft rejection, arteriogenesis, renal disease, psoriasis, and during pregnancy.
Silverman et.al. demonstrated the presence of FKN in normal cultured microvascular endothelial and stromal cells of iris and retina in vitro. Upon inflammatory cytokine stimulation, EC also express FKN and its receptors with FKN secretion in an autocrine manner. In addition to EC chemotaxis and tube formation, FKN is an angiogenic mediator in rheumatoid arthritis.