Oestrogen inhibits psoriasis‐like dermatitis induced by imiquimod in mice in relation to increased IL‐10 producing cells despite elevated expression of IL‐22, IL‐23, IL‐17 mRNA

Abstract Sex hormones influence the development and natural course of psoriasis. Here, we examined the effects of female sex hormones, particularly oestrogen, on psoriasis‐like dermatitis induced using topical imiquimod in mice that underwent either sham operation (Sham) or ovariectomy (OVX), with (hormone replacement treatment: HRT) or without 17β‐oestradiol targeting the maximum physiological levels. The number of neutrophils in the skin was higher in the order of OVX‐, Sham‐, and HRT‐treated mice. However, no significant difference was detected in the clinical scores among the three groups due to severe erythema and scale in a few mice out of HRT‐treated mice in a set of experiments. OVX‐ and HRT‐treated mice showed increased mRNA levels of interleukin ( IL )‐ 22 and IL‐23 compared with Sham‐treated mice; increased IL‐10 mRNA levels were found in HRT‐treated mice, possibly due to an increased proportion of forkhead box P3 (Foxp3)‐ and IL‐10 positive large cells (possibly macrophages). In addition, HRT‐treated mice had a more compact stratum corneum with higher expression of loricrin and involucrin than OVX‐ and Sham‐treated mice. This study suggests that oestrogen has a dual potential in the pathogenesis of psoriasis: suppression of inflammation by enhancing IL‐10 production and enhancement of inflammation by induction of IL‐22 and IL‐23 expression.