Vitamin D (vD) levels have been reported to correlate with (a) lung function in healthy populations and (b) disease severity in pulmonary TB, COPD and asthma. The proposed mechanism, supported by in vitro studies, relates to vD response elements in the promoter regions of genes encoding molecules involved in innate immunity such as defensins and cathelicidin (LL-37). As patients with CF are at risk of fat and fat-soluble vitamin malabsorption, we sought to explore this relationship in a cohort of CF children. Frozen serum and bronchoalveolar (BAL) fluid samples, which had been donated for research at the time of a clinically-indicated bronchoscopy were available from 49 children with CF. Mean age at the time of the procedure was 6.8 years (range 0.03–15.99). 44 (90%) were biochemically pancreatic insufficient and were prescribed pancreatic enzyme supplementation and fat-soluble mulitvitamins. Serum 25OH vD3 was measured using HPLC and mass spectrometry. BALF human beta defensin-2 (hbD2) and LL-37 were quantified using ELISA. vD deficiency was defined as <20 ng/ml based on internationally-accepted criteria. Deficient and sufficient groups were compared with Mann–Whitney tests and Spearman's correlations were performed. 16 (33%) children were vD-deficient (including two of the five pancreatic sufficient patients); they did not differ in age from the vD sufficient group. BALF hbD2 was significantly lower than in the vD sufficient group (median (range) 185.3 (7.8–615.7) pg/ml vs 385.5 (7.8–1002) pg/ml; p<0.05). In contrast, no relationship was observed between serum vD and BAL LL-37. As this molecule is known to be highly sensitive to proteolysis, we considered the possibility that degradation could be masking an effect of vD on LL-37 expression. However, no inverse relationship with neutrophil elastase or MMP-9 was found to support this hypothesis. Children with CF are at risk of low vD levels even if they are clinically pancreatic sufficient or if vitamin supplements are being prescribed. vD deficiency is associated with low levels of antimicrobial defence molecules within the airway. Whether this is a clinically important phenomenon leading to susceptibility to infection and increased inflammation will be the focus of future work.
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