A developing HPA axis permits neonatal immune sensitivity to common allergens [scRNA-Seq]
Atopic and allergic diseases predominantly manifest in early life, a period of profound growth and maturation. Yet, there is a dearth of information on the impact of developmental parameters on the neonatal immune reaction to allergens. Here we demonstrate that common allergens including house dust mite (HDM) elicited potent type 17 inflammatory responses from neonatal but not adult mice. HDM-induced inflammation was abolished in Rorgt-, gd T cell-, or epithelial IL-17RC- deficient animals and surprisingly did not require nociceptors or lymph node engagement. Instead, neonatal CD301b+ type 2 conventional dendritic cells (cDC2s) abundantly engulfed allergen and locally activated gd T cells in the skin. Despite uptaking equivalent antigen to neonates, adult cDC2s did not promiscuously activate in the skin. Mechanistically, this discrepancy was not attributable to cell-intrinsic differences arising from the distinct developmental origins of neonatal and adult cDC2s. Instead, neonatal cDC2 hyperactivation could be traced to a lower systemic glucocorticoid level, a consequence of an immature hypothalamic-pituitary-adrenal (HPA) axis in early life, and could be reversed by cortisol administration at the time of allergen challenge. These findings bring to fore the influence of organismal developmental factors in shaping immune sensitivity to allergens in early life. Overall design: To dissect the baseline composition of  antigen presenting cell populations  we isolated immune cells from neonate and adult dorsal skin and performed single cell RNA sequencing. To characterize the activation of dendritic cells in house dust mite (HDM) treated neonate skin, we performed single cell RNA sequencing with neonate skin cells isolated 9 hours after PBS and HDM inoculation.