Atopic dermatitis (AD) is a common allergic inflammatory skin disease caused by a combination of intense pruritus, scratching, and epicutaneous (e.c.) sensitization with allergens. To explore the roles of IL-21 and IL-21 receptor (IL-21R) in AD, we examined skin lesions from patients with AD and used a mouse model of allergic skin inflammation. IL-21 and IL-21R expression was upregulated in acute skin lesions of AD patients and in mouse skin subjected to tape stripping, a surrogate for scratching. The importance of this finding was highlighted by the fact that both Il21r–/– mice and WT mice treated with soluble IL-21R–IgG2aFc fusion protein failed to develop skin inflammation after e.c. sensitization of tape-stripped skin. Adoptively transferred OVA-specific WT CD4+ T cells accumulated poorly in draining LNs (DLNs) of e.c. sensitized Il21r–/– mice. This was likely caused by both DC-intrinsic and nonintrinsic effects, because trafficking of skin DCs to DLNs was defective in Il21r–/– mice and, to a lesser extent, in WT mice reconstituted with Il21r–/– BM. More insight into this defect was provided by the observation that skin DCs from tape-stripped WT mice, but not Il21r–/– mice, upregulated CCR7 and migrated toward CCR7 ligands. Treatment of epidermal and dermal cells with IL-21 activated MMP2, which has been implicated in trafficking of skin DCs. These results suggest an important role for IL-21R in the mobilization of skin DCs to DLNs and the subsequent allergic response to e.c. introduced antigen.
Haoli Jin, Michiko K. Oyoshi, Yi Le, Teresa Bianchi, Suresh Koduru, Clinton B. Mathias, Lalit Kumar, Séverine Le Bras, Deborah Young, Mary Collins, Michael J. Grusby, Joerg Wenzel, Thomas Bieber, Marianne Boes, Leslie E. Silberstein, Hans C. Oettgen, Raif S. Geha