Cysteinyl leukotriene receptor 2, also termed CYSLTR2, is a receptor for cysteinyl leukotrienes (LT) (see leukotrienes#Cysteinyl leukotrienes). CYSLTR2, by binding these cysteinyl LTs (CysLTs; viz, LTC4, LTD4, and to a much lesser extent, LTE4) contributes to mediating various allergic and hypersensitivity reactions in humans. However, the first discovered receptor for these CsLTs, cysteinyl leukotriene receptor 1 (CysLTR1), appears to play the major role in mediating these reactions. Gene The human gene maps to the long arm of chromosome 13 at position 13q14, a chromosomal region that has long been linked to asthma and other allergic diseases. The gene consists of four exons with all introns located in the genes' 5' UTR region and the entire coding region located in the last exon. CysLTR2 encodes a protein composed of 347 amino acids and shows only modest similarity to the CysLTR1 gene in that its protein shares only 31% amino acid identity with the CysLTR1 protein. Receptor CySLTR2 mRNA is co-expressed along with CysLRR1 in human blood eosinophils and platelets, and tissue mast cells, macrophages, airway epithelial cells, and vascular endothelial cells. It is also expressed without CysLTR1 throughout the heart, including Purkinje cells, adrenal gland, and brain as well as some vascular endothelial, airway epithelial, and smooth muscle cells. CysLTR2, similar to CysLTR1, is a G protein–coupled receptor that links to and when bound to its CysLT ligands activates the Gq alpha subunit and/or Ga subunit of its coupled G protein, depending or the cell type. Acting through these G proteins and their subunits, ligand-bound CysLTR1 activates a series of pathways that lead to cell function (see Gq alpha subunit#function and Ga subunit#function for details); the order of potency of the cysLTs in stimulating CysLTR2 is LTD4=LTC4>LTE4 with LTE4 probably lacking sufficient potency to have much activity that operates through CysLTR1 in vivo. By comparison, the stimulating potencies of these CysLTs for CysLTR1 is LTD4>LTC4>LTE4 with LTD4 showing 10-fold greater potency on CysLTR1 than CysLTR2. Perhaps related to this difference in CysLT sensitivities, cells co-expressing CysLTR2 and CysLTR1 may exhibit lower sensitivity to LTD4 than do cells expressing only CysLTR1; in consequence, CysLTR2 has been suggested to dampen CysLTR1's activities. In addition to CysLTR1, GPR99 (also termed the oxoglutarate receptor or, sometimes, CysLTR3) appears to be an important receptor for CysLTs, particularly for LTE4: the CystLTs show relative potencies of LTE4>LTC4>LTD4 in stimulating GPR99-bearing cells and GPR99-deficient mice exhibit a dose-dependent