Vitamin D supplementation of initially vitamin D‐deficient mice diminishes lung inflammation with limited effects on pulmonary epithelial integrity

In disease settings, vitamin D may be important for maintaining optimal lung epithelial integrity and suppressing inflammation, but less is known of its effects prior to disease onset. Female BALB /c dams were fed a vitamin D 3 ‐supplemented (2280 IU/kg, VitD + ) or nonsupplemented (0  IU /kg, VitD − ) diet from 3 weeks of age, and mated at 8 weeks of age. Male offspring were fed the same diet as their mother. Some offspring initially fed the VitD − diet were switched to a VitD + diet from 8 weeks of age (VitD −/+ ). At 12 weeks of age, signs of low‐level inflammation were observed in the bronchoalveolar lavage fluid ( BALF ) of VitD − mice (more macrophages and neutrophils), which were suppressed by subsequent supplementation with vitamin D 3 . There was no difference in the level of expression of the tight junction proteins occludin or claudin‐1 in lung epithelial cells of VitD + mice compared to VitD − mice; however, claudin‐1 levels were reduced when initially vitamin D‐deficient mice were fed the vitamin D 3 ‐containing diet (VitD −/+ ). Reduced total IgM levels were detected in BALF and serum of VitD −/+ mice compared to VitD + mice. Lung mRNA levels of the vitamin D receptor ( VDR ) were greatest in VitD −/+ mice. Total IgG levels in BALF were greater in mice fed the vitamin D 3 ‐containing diet, which may be explained by increased activation of B cells in airway‐draining lymph nodes. These findings suggest that supplementation of initially vitamin D‐deficient mice with vitamin D 3 suppresses signs of lung inflammation but has limited effects on the epithelial integrity of the lungs.