Vitamin D modulates the allergic phenotype of dendritic cells in children with atopic dermatitis

Vitamin D (VD) deficiency has been associated with increased incidence and severity of atopic dermatitis (AD), but the mechanisms through which VD may ameliorate AD are unclear. We compared the phenotypic characteristics of circulating myeloid and plasmacytoid dendritic cells (mDCs and pDCs, respectively) of children with AD vs healthy controls (HC) and evaluated if VD can modulate the allergic phenotype of circulating DCs in AD patients. Although there was no difference in frequency of circulating DCs between groups, among children with AD there was an inverse correlation between SCORAD and circulating total DCs and mDCs. In AD, serum IgE concentration correlated with FcεRI and surface-bound IgE expression on mDCs and pDCs; pDCs expressing FcεRI and IgE were significantly increased compared to HC. Ex vivo, 1,25(OH)₂ D₃ significantly decreased FcεRI expression on mDCs and surface-bound IgE on mDCs and pDCs. Oral VD supplementation reduced expression of surface-bound IgE on pDCs in children with AD. In summary, VD decreases the allergic phenotype of circulating DCs in children with AD, a potential mechanism for how VD supplementation may improve AD severity. Future studies are needed to further assess the role of VD supplementation as an immunomodulatory therapy for AD.