Dedicator of cytokinesis 8 (DOCK8) is a negative regulator of skin mast cell function

Abstract Dysregulated expansion and/or activation of mast cells have detrimental consequences in allergic disease. In humans, homozygous or compound heterozygous deletions of DOCK8 cause a combined immunodeficiency characterized by allergic disorders. Based on this evidence, we hypothesized that DOCK8 may be a negative regulator of mast cell function. To address this hypothesis, we used mice with a loss-of-function mutation in Dock8 (primuris, Dock8 pri/primice) and conditional mice in which DOCK8 is ablated in connective tissue mast cells (Mcpt5-Cre +; Dock8 fl/flmice). Dock8 pri/primice exhibited increased plasma levels of mast cell protease-1 (MCPT1) in homeostatic conditions. Furthermore, Dock8 pri/primice and Mcpt5-Cre +; Dock8 fl/flmice experienced a more severe IgE-dependent passive cutaneous anaphylactic reaction (PCA) than control mice. This data suggests that DOCK8 deficiency is linked to increased mast cell activation in homeostatic conditions and upon stimulation by IgE-dependent mechanisms. Fetal skin derived cultured mast cells (FSMCs) generated from Dock8 pri/primice released increased amounts of β-hexosaminidase upon IgE-dependent activation. Consistent with this finding, naïve DOCK8-deficient FSMCs exhibited alterations in cytoskeletal dynamics that may facilitate mast cell degranulation. Finally, we observed an increased number of tryptase positive cells in skin biopsies obtained from three pediatric patients diagnosed with hyper IgE syndrome (HIES) due to DOCK8 mutations, suggesting that DOCK8 immunodeficiency may contribute to skin mast cell expansion in humans. Our findings provide strong evidence that DOCK8 can contribute to negative regulation of skin mast cell activation and expansion. R01 AI140626-05