The CCR1 receptor is a member of the beta chemokine receptor family (GPCR-A1). Chemokines and their receptors are critical for the recruitment of effector immune cells to the site of inflammation. The ligands of this receptor include macrophage inflammatory protein 1 alpha (MIP-1 alpha), regulated on activation normal T expressed and secreted protein (RANTES), monocyte chemoattractant protein 3 (MCP-3), and myeloid progenitor inhibitory factor-1 (MPIF-1). Following interaction with their specific chemokine ligands, chemokine receptors trigger a flux in intracellular calcium (Ca2+) ions (calcium signaling). This causes cell responses, including the onset of a process known as chemotaxis that traffics the cell to a desired location within the organism.
CXC chemokine receptors are integral membrane proteins (GPCR-A2) that specifically bind and respond to cytokines of the CXC chemokine family. CXCR1 and CXCR2 (IL8R-α and IL8R–β respectively) are closely related receptors that recognize CXC chemokines that possess an E-L-R amino acid motif immediately adjacent to their CXC motif; they are both expressed on the surface of neutrophils in mammals. While CXCR3 is expressed predominantly on T lymphocytes, the CXCR4 receptor has a wide cellular distribution, with expression on most immature and mature hematopoietic cell types[1].
Fractalkine is a transmembrane protein and chemokine involved in the adhesion and migration of leukocytes. The protein encoded by this gene is a receptor for fractalkine (CX3CR1). CX3CR1 and its ligand help control the migration and recruitment of immune effector cells in numerous inflammatory diseases and may play a role in cancer progression, immune evasion, and metastasis. Increasing evidence indicates that CX3CR1 is required for monocyte homeostasis and differentiation and regulates the fate of monocyte-derived cells in other inflammatory diseases such as cardiovascular disease and liver fibrosis. However, precisely how CX3CR1 regulates tumor-associated macrophages (TAMs) subtypes in the tumor microenvironment remains unknown[2]. Besides, evidence is found that the fractalkine receptor also is a coreceptor for HIV-1, and some variations in this gene lead to increased susceptibility to HIV-1 infection and rapid progression to AIDS[3].
The CC chemokine receptor 8 (CCR8) belongs to the seven transmembrane-spanning receptor family and functionally responds to the eukaryotic CC chemokines I-309, thymus and activation-regulated chemokine, macrophage inflammatory protein-1 beta (MIP-1b) and to the products viral MIP-I and viral MIP-II of the Kaposi-associated herpesvirus (HHV-8).[4]