Accumulation of CRTH2-positive T-helper 2 and T-cytotoxic 2 cells at implantation sites of human decidua in a prostaglandin D₂-mediated manner

T-helper (Th) 2-type cytokines predominate in decidua, plausibly accounting for protection of a semiallograft, the embryo and placenta, from attack by the maternal immune system. However, localization of Th2 and T-cytotoxic (Tc) 2 cells in decidua has not been reported, presumably because of the difficulty in detecting intracellular cytokines in tissues. Here, by staining tissues for a novel surface maker of Th2/Tc2, the chemoattractant receptor-homologous molecule CRTH2, which is expressed on Th2 cells, we show that CRTH2⁺ Th2 cells and CRTH2⁺ Tc2 cells are significantly increased at the materno-fetal interface (implantation site) in decidua. We also show that trophoblast, uterine epithelium and endometrial glands all express haematopoietic-type prostaglandin (PG) D₂ synthase (hPGDS). Since CRTH2 is a chemoattractant receptor for PGD₂ and mediates PGD₂-dependent migration of blood Th2 cells, our findings suggest that Th2 and Tc2 cells may be recruited to the materno-fetal interface, at least in part in a PGD₂-mediated manner.