Mechanisms of vitamin D3 metabolite repression of IgE-dependent mast cell activation

Background Mast cells have gained notoriety based on their detrimental contributions to IgE-mediated allergic disorders. Although mast cells express the vitamin D receptor (VDR), it is not clear to what extent 1α,25-dihydroxyvitamin D 3 (1α,25[OH] 2 D 3 ) or its predominant inactive precursor metabolite in the circulation, 25-hydroxyvitamin D 3 (25OHD 3 ), can influence IgE-mediated mast cell activation and passive cutaneous anaphylaxis (PCA) in vivo . Objective We sought to assess whether the vitamin D 3 metabolites 25OHD 3 and 1α,25(OH) 2 D 3 can repress IgE-dependent mast cell activation through mast cell–25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) and mast cell–VDR activity. Methods We measured the extent of vitamin D 3 suppression of IgE-mediated mast cell degranulation and mediator production in vitro , as well as the vitamin D 3 –induced curtailment of PCA responses in WBB6F 1 - Kit W/W-v or C57BL/6J- Kit W-sh/W-sh mice engrafted with mast cells that did or did not express VDR or CYP27B1. Results Here we show that mouse and human mast cells can convert 25OHD 3 to 1α,25(OH) 2 D 3 through CYP27B1 activity and that both of these vitamin D 3 metabolites suppressed IgE-induced mast cell–derived proinflammatory and vasodilatory mediator production in a VDR-dependent manner in vitro . Furthermore, epicutaneously applied vitamin D 3 metabolites significantly reduced the magnitude of skin swelling associated with IgE-mediated PCA reactions in vivo ; a response that required functional mast cell–VDRs and mast cell–CYP27B1. Conclusion Taken together, our findings provide a mechanistic explanation for the anti-inflammatory effects of vitamin D 3 on mast cell function by demonstrating that mast cells can actively metabolize 25OHD 3 to dampen IgE-mediated mast cell activation in vitro and in vivo .