osed circles–OVA/vehicle cohort and open circles–OVA/Compound A cohort. Each point shown is the mean 6 SEM. Mice were epicutaneously sensitized to PBS or OVA and dosed with either drug vehicle or Compound A on days 17. After removing the skin patches on day 7, the mice were left unmanipulated until day 24, at which time the spleen was isolated and serum was drawn. OVA-specific IgE and IgG1 serum levels were determined. The spleen cells were cultured at 2 3 106 splenocytes per well of a 96-well round-bottom plate in the presence of 1 lg ml1 OVA for 72 h. Supernatants were harvested and analyzed by ELISA for IL-17A, IL-13 and IFN-c. The value from each individual mouse is shown, and the horizontal bars represent the median. Spleen sections from mice treated as in were stained with PNA to show areas of activated B lymphocytes in the lymphoid follicles. 12 CRTH2 blocks OVA-induced skin inflammation inflammatory response seen with Compound A-treated mice in two models of allergic dermatitis. Discussion AD is a common inflammatory skin disease with lesions characterized by epidermal thickening and a prominent perivascular and dermal infiltrate, as well as high serum IgE levels. In this study, we used two well-characterized murine models of AD to examine the role of CRTH2 in JW-55 cutaneous inflammation. Both of these models are CD4+ T lymphocyte dependent, as is AD. In a model of repeated epicutaneous sensitization, the administration of a CRTH2 antagonist reduced inflammation in the dermis substantially, as 
well as prevented epidermal thickening. Using a robust 25 day FITC model of contact hypersensitivity, the administration of the CRTH2 antagonist just prior to challenge substantially blocked ear swelling. Additionally, administration of Compound A from days 14 to 25 inhibited inflammation further still, reducing ear thickness;75% compared with untreated controls. Importantly, an examination of serum Ig levels showed a decrease in total IgE in animals treated with the CRTH2 antagonist in both in PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19826300 vivo models. Further, in the epicutaneous OVA sensitization model, where antigen-specific antibody levels could reliably be measured, there was a decrease in OVA-specific IgE, IgG1 and IgG2a levels. A closer examination of this was carried by epicutaneously sensitizing mice to OVA for a 1-week period while administering drug vehicle or Compound A. Again, an antigen-specific decrease was seen in the IgE, IgG1 and IgG2a Ig classes upon administration of the CRTH2 antagonist. As antibody titers to protein antigens rise substantially with repeated immunizations, the effect of Compound A became more pronounced. Hence, we observed a much greater effect on Ig levels in the chronic OVA model, with Compound A administered during the second and third patching than after the first patching. It should also be pointed out that antibody production was not affected by the CRTH2 antagonist following intra-peritoneal immunization with same protein antigen, ovalbumin, emulsified in the adjuvant alum. This suggests that the route of antigen delivery and subsequent presentation may play a key role in determining the influence of a CRTH2 blockade. These findings confirm and extend the findings of Nakamura et al. using a CRTH2/ mice bred to the BALB/c background. They initially reported a modest decrease in total IgE levels in CRTH2/ mice following multiple cutaneous sensitizations with TNCB. This slight decrease may be attributable to the fact that this model is not T cell