Methods: GRP-deficient-IL-13-Tg-mice (IL-13Tg(+)/GRP-/-) was generated by crossbreeding GRP-/-knockout mice with K5-tTA-IL-13 mice (C576/BL/6 background). IL-13 is inducibly activated in the skin under keratin-5 (K5) promoter. The time to the onset of AD, AD Score, itch/scratch behavior, dermal cytokines and serum IgE levels by ELISA were evaluated. Histopathological assessments (IHC, H&E, and Toluidine blue staining) of dermal infiltrate were performed. Expression of GRP by IF was determined using skin biopsy samples from AD patients and normal subjects.
Results: The expression of GRP was markedly enhanced in lesional skin of IL-13-induced AD and in dermal inflammatory cells and PGP9.5+ afferents in human AD skin, but not in the skin of control subjects. Compared to IL-13Tg(+)/GRP+/+ mice, IL-13Tg(+)/GRP–/–mice had significantly delayed onset of AD (P<0.01), attenuated itch-evoked scratching behaviors (P<0.01), reduced serum IgE levels (P<0.05), and substantially reduced dermal inflammatory responses. Deletion of GRP did not alter the transgene IL-13 activation.
Conclusions: GRP is highly expressed in human AD skin and in IL-13-induced AD skin. Deletion of GRP in IL-13 Tg mice markedly attenuated the AD phenotype, suggesting that GRP contributes to the onset of AD, generation of pruritus and Th2 immune response induced by IL-13.