Vitamin D binding protein and vitamin D in human allergen-induced endobronchial inflammation

Allergic asthma is a chronic disease of the airways associated with airway hyperresponsiveness, a variable degree of airflow obstruction, airway remodelling and a characteristic airway inflammation. Factors of the vitamin D axis, which include vitamin D metabolites and vitamin D binding protein (VDBP), have been linked to asthma, but only few data exist about their regulation in the lung during acute allergen-induced airway inflammation. Therefore, we analysed the regulation of factors of the vitamin D axis during the early- and late-phase reaction of allergic asthma. Fifteen patients with mild allergic asthma underwent segmental allergen challenge. VDBP was analysed in bronchoalveolar lavage fluid (BALF) and serum using the enzyme-linked immunosorbent assay (ELISA) technique. 25-hydroxyvitamin D3 [25(OH)D3] and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] were analysed by a commercial laboratory using the liquid chromatography-mass spectrometry (LC/MS) technique. VDBP (median 23, range 02-71g/ml), 25(OH)D3 (median 0060, range<0002-3210ng/ml) and 1,25(OH)2D3 (median<01, range<01-28pg/ml) were significantly elevated in BALF 24h but not 10min after allergen challenge. After correction for plasma leakage using the plasma marker protein albumin, VDBP and 25(OH)D3 were still increased significantly while 1,25(OH)2D3 was not. VDBP and 25(OH)D3 were correlated with each other and with the inflammatory response 24h after allergen challenge. Serum concentrations of all three factors were not influenced by allergen challenge. In conclusion, we report a significant increase in VDBP and 25(OH)D3 in human BALF 24h after allergen challenge, suggesting a role for these factors in the asthmatic late-phase reaction.