Vitamin D regulation of OX40 ligand in immune responses to Aspergillus fumigatus.

OX40 ligand (OX40L) is a costimulatory molecule involved in Th2 allergic responses. It has been shown that vitamin D deficiency is associated with increased OX40L expression in peripheral CD11c(+) cells and controls Th2 responses to Aspergillus fumigatus in vitro in cystic fibrosis (CF) patients with allergic bronchopulmonary aspergillosis (ABPA). To investigate if vitamin D deficiency regulated OX40L and Th2 responses in vivo, we examined the effect of nutritional vitamin D deficiency on costimulatory molecules in CD11c(+) cells and A. fumigatus-induced Th2 responses. Vitamin D-deficient mice showed increased expression of OX40L on lung CD11c(+) cells, and OX40L was critical for enhanced Th2 responses to A. fumigatus in vivo. In in vitro assays, vitamin D treatment led to vitamin D receptor (VDR) binding in the promoter region of OX40L and significantly decreased the promoter activity of the OX40L promoter. In addition, vitamin D altered NF-κB p50 binding in the OX40L promoter that may be responsible for repression of OX40L expression. These data show that vitamin D can act directly on OX40L, which impacts Th2 responses and supports the therapeutic use of vitamin D in diseases regulated by OX40L.