Age-related changes in vitamin D metabolism and vitamin D receptor expression in equine alveolar macrophages: A preliminary study

The vitamin D receptor (VDR)-vitamin D axis modulates pulmonary immunity in people but its role in equine immunity is unknown. Bacterial pneumonia causes high morbidity/mortality in foals and alveolar macrophages (AM phi) are important for pulmonary defenses. Age-related variations in vitamin D-mediated function of AM phi might contribute to the foal's susceptibility to pneumonia. Our aim was to assess the impact of age on equine vitamin D metabolism and VDR expression in AM phi. AM phi and plasma was collected from healthy foals (2, 4 and 8 weeks old) and adult horses (once). AM phi VDR expression was determined via RT-qPCR and plasma vitamin D metabolites quantified via immunoassays. Data were analyzed with linear mixed models. Inactive-vitamin D metabolite concentrations were lowest in foals at 2 weeks and lower at 2 and 4 weeks compared to adults (P < 0.001). Active-vitamin D metabolite concentrations were higher in foals than adults (P < 0.05). VDR expression was detected in AM phi in all animals and was highest in 2-week-old foals. Vitamin D metabolism and AM phi VDR expression are impacted by age in horses. This may have immunological consequences in foals given the key role that the VDR-vitamin D axis has in pulmonary immunity in other species.

Automated summary

This study assessed the impact of age on equine vitamin D metabolism and VDR expression in alveolar macrophages (AM phi), and found that both vitamin D metabolism and VDR expression in horses are influenced by age, which may have implications for pulmonary immunity in foals.