It is thought that these receptors have contrasting effects in AD, with PGD2-DP1 signaling acting to reduce inflammation and preserve barrier function whereas PGD2-CRTH2 signaling acts to induce chemotaxis in leukocytes and promotes an inflammatory response.40,41 Although the important role of PGD2 in AD is evident, there is limited research in the role of early life PGD2 in the development of childhood AD. The gene discussed is PTGDR2; the disease is Alzheimer disease.