Receptor for prostaglandin D2 (PGD2). Coupled to the G(i)- protein. Receptor activation may result in pertussis toxin-sensitive decreases in cAMP levels and Ca(2+) mobilization. PI3K signaling is also implicated in mediating PTGDR2 effects. PGD2 induced receptor internalization. CRTH2 internalization can be regulated by diverse kinases such as, PKC, PKA, GRK2, GPRK5/GRK5 and GRK6. Receptor activation is responsible, at least in part, in immune regulation and allergic/inflammation responses. {ECO:0000269|PubMed:11208866, ECO:0000269|PubMed:11535533, ECO:0000269|PubMed:17196174}. This is the function of PTGDR2 (prostaglandin D2 receptor 2, Ensembl gene identifier ENSG00000183134).