vitro responses of cells involved in allergic reactions as well as the in vivo allergic responses in animal models as that induced by CysLT-induced CysLTR1 (see Cysteinyl leukotriene receptor 1#Receptor. However, CysLT2 requires 10-fold higher concentrations of LTD4, the most potent cysLT for CysLTR1, to activate CysLTR2. Furthermore, the allergic and hypersensitivity responses of humans and animal models are significantly reduced by chronic treatment with Montelukast, Zafirlukast, and Pranlukast, drugs which are selective receptor antagonists of CysLTR1 but not CysLTR2. Models of allergic reactions in Cysltr2-deficient mice as well as in a human mast cell line indicate that mouse Cysltr2 and its human homolog CysLTR2 act to inhibit Cysltr1 and CysLTR1, respectively, and therefore suggest that CysLTR2 may similarly inhibit CysLTR1 in human allergic diseases. The role of CysLTR2 in the allergic and hypersensitivity diseases of humans must await the development of selective CysLTR2 inhibitors. See also Cysteinyl leukotriene receptor 1 Eicosanoid receptor GPR99 References Further reading External links G protein-coupled receptors