Tu100 - The Role of the CH25H/EBI2 Axis in the Recruitment of Mast Cell Progenitors During Type 2 Inflammation

Abstract Text: Basophils, eosinophils, and mast cells (MCs) are granulocytes which expand in the airways during Type 2 Inflammation (T2I) -associated diseases, where they are thought to play a major role in disease pathobiology. While the chemotactic signals responsible for recruitment of basophils and eosinophils to the inflamed tissue are well characterized, the signals directing MC progenitor (MCp) recruitment remained unknown. Single-cell RNA sequencing of human peripheral MCps reviled high expression levels of Gpr183, encoding the receptor EBI2. Venous endothelial cells in human sinus tissue and asthmatic airways exhibit high expression of cholesterol 25-hydroxylase (CH25H), an enzyme necessary for production of EBI2 ligands. Mouse MCps and mouse endothelial cells exhibit similar expression pattern of Gpr183 and Ch25h. To further assess the role of the Ch25h/EBI2 axis in pulmonary MC expansion, we adapted an approach, in which mice were IV-injected with FITC-labelled anti-CD45 to distinguish immune cells within the vasculature, versus immune cells within the lung parenchyma to track MCp recruitment upon aeroallergen challenge. Following dust mite-induced allergic lung inflammation, we find that MCps in WT mice are quickly recruited to the lung parenchyma and retained, where they undergo phenotypic maturation. In contrast, MCp recruitment to the lung parenchyma was reduced by 97% in mice with a targeted deletion of EBI2 in hematopoietic cells (Vav1Cre; EBI2FL/FL ) and by 95% in ch25h deficient mice. EBI2/Ch25h deficiency had little to no effect on basophil or eosinophil recruitment, suggesting a selective role for the EBI2/Ch25h axis, in directing MCp recruitment from the vasculature during T2I.