Involvement of estrogen receptor α in pro-pruritic and pro-inflammatory responses in a mouse model of allergic dermatitis.

It has been reported that endogenous or exogenous estrogens can affect the immune system, resulting in immune disorders; however, their direct involvement in such conditions remains to be demonstrated. The purpose of this study was to investigate whether estrogen receptors (ER) are directly implicated in pro-pruritic and pro-inflammatory reactions in cutaneous allergy. Initially, enhancement of the pro-inflammatory response by several ER agonists [methoxychlor (MXC), β-estradiol (E2), propylpyrazoletriol (PPT; an ERα agonist), and diarylpropionitrile (DPN; an ERβ agonist)] was examined in vivo using a male BALB/c mouse model of allergic dermatitis induced by toluene-2,4-diisocyanate administration. The ear swelling response, itch response, and local cytokine secretion were measured. Subsequently, the mechanism underlying the development of such allergic reactions was analyzed in vitro using human epidermal keratinocytes, murine bone marrow-derived dendritic cells (mBMDCs), and the mixed leucocyte reaction assay. Activated cells were exposed to each ER agonist for 24 h, and cytokine secretion and cell proliferation were measured. Our in vivo experiments indicated significant upregulation of pro-inflammatory and pro-pruritic responses in the E2-, MXC-, and PPT-treated groups compared to the control group; however, no change was observed in the DPN-treated group. Levels of cytokines expressed by keratinocytes, such as TSLP and IL-33, were particularly increased by exposure to E2, MXC, or PPT. These in vivo results were confirmed in vitro in keratinocytes, but not mBMDCs or T cells. Our findings imply that ERα is involved in pro-inflammatory and pro-pruritic responses in cutaneous allergy through activation of keratinocytes.