PGD2 binds to smooth muscle cells leading to vasodilatation and bronchoconstriction and can also bind the chemoattractant receptor-homologous molecule expressed on TH2 lymphocytes (CRTH2) inducing Th2 cytokine production and further promoting activation of MCs and PGD2 production in asthma (64). This evidence concerns the gene PTGDR2 and asthma.