title: The prostaglandin D₂ receptor CRTH2 is important for allergic skin inflammation after epicutaneous antigen challenge.
abstract: BACKGROUND
  Cutaneous prostaglandin (PG) D₂ levels increase after scratching. Chemoattractant receptor-homologous molecule expressed on receptor on T(H)2 cells (CRTH2) mediates chemotaxis to PGD₂ and is expressed on T(H)2 cells and eosinophils, which infiltrate skin lesions in patients with atopic dermatitis.
  
  
  OBJECTIVE
  We sought to examine the role of CRTH2 in a murine model of atopic dermatitis.
  
  
  METHODS
  CRTH2(-/-) mice and wild-type control animals were epicutaneously sensitized by means of repeated application of ovalbumin (OVA) to tape-stripped skin for 7 weeks and then challenged by means of OVA application to tape-stripped previously unsensitized skin for 1 week. Skin histology was assessed by means of hematoxylin and eosin staining and immunohistochemistry. Cytokine mRNA expression was examined by means of quantitative RT-PCR. Levels of PGD₂, antibody, and cytokines were measured by means of ELISA.
  
  
  RESULTS
  PGD₂ levels significantly increased in skin 24 hours after tape stripping, although not in skin subjected to repeated sensitization with OVA. Allergic skin inflammation developed normally at sites of chronic epicutaneous sensitization with OVA in CRTH2(-/-) mice but was severely impaired in previously unsensitized skin challenged with OVA, as evidenced by significantly decreased skin infiltration with eosinophils and CD4(+) cells and impaired T(H)2 cytokine mRNA expression. Impaired skin inflammation at sites of acute OVA challenge in CRTH2(-/-) mice was not due to an impaired systemic response to epicutaneous sensitization because OVA-specific IgG1 and IgE antibody levels and OVA-driven splenocyte secretion of cytokines in these mice were comparable with those seen in wild-type control animals.
  
  
  CONCLUSIONS
  CRTH2 promotes allergic skin inflammation in response to cutaneous exposure to antigen in previously sensitized mice.
authors: Division of Immunology, Children's Hospital and Department of Pediatrics, Harvard Medical School, Boston, MA, USA.
authors: Rui
authors: R
authors: He
authors: Michiko K
authors: MK
authors: Oyoshi
authors: James Y T
authors: JY
authors: Wang
authors: Martin R
authors: MR
authors: Hodge
authors: Haoli
authors: H
authors: Jin
authors: Raif S
authors: RS
authors: Geha
mesh_terms: D000279:Administration, Cutaneous; D000818:Animals; D002634:Chemotaxis, Leukocyte; D003876:Dermatitis, Atopic / Q000276:immunology* / Q000473:pathology; D005260:Female; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D010047:Ovalbumin / Q000008:administration & dosage* / Q000276:immunology; D015230:Prostaglandin D2 / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism*; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D012867:Skin / Q000276:immunology / Q000473:pathology; D018418:Th2 Cells / Q000276:immunology
chemical_list: D011971:Receptors, Immunologic; D011982:Receptors, Prostaglandin; D010047:Ovalbumin; D015230:Prostaglandin D2; C036293:prostaglandin D2 receptor