Longitudinal Evaluation of Vitamin D, Parathyroid Hormone, Antimicrobial Peptides, and Immunomodulatory Genes in Hospitalized Foals.

BACKGROUND: Information about the association of antimicrobial peptides with hypovitaminosis D in hospitalized foals is lacking. HYPOTHESIS/OBJECTIVES: We aimed to longitudinally determine the association of serum concentrations of vitamin D metabolites, vitamin D binding protein (DBP), and parathyroid hormone (PTH) with antimicrobial peptides (β-defensin-1 and cathelicidin-1) and the mRNA expression of the vitamin D receptor (VDR), 1α-hydroxylase (CYP27B1), 24-hydroxylase (CYP24A1), toll-like receptor-4 (TLR-4), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), disease severity, and mortality in hospitalized foals. We hypothesized that hypovitaminosis D would be associated with decreased serum concentrations of antimicrobial peptides, disease severity, and mortality in hospitalized foals. ANIMALS: One hundred nine foals ≤ 72 h of age divided into hospitalized (n = 83; 60 septic, 23 sick nonseptic [SNS]) and healthy (n = 26) foals. METHODS: Blood samples were collected on admission (0), and 24, 48, and 72 h after admission from healthy and hospitalized foals. Data were analyzed by repeated measure methods. RESULTS: Serum 25(OH)D, 1,25(OH)D, DBP, β-defensin-1, and cathlicidin-1 concentrations were significantly lower, whereas PTH concentrations were higher in hospitalized compared to healthy foals at different times during hospitalization (p < 0.05). Septic foals had lower VDR and CYP27B1, but higher TLR-4, TNF-α, and IL-1β mRNA expression than in healthy foals (p < 0.05). Decreased serum 25(OH)D, β-defensin-1, and cathelicidin-1, and high PTH concentrations were associated with higher odds of death in hospitalized foals (p < 0.05). CONCLUSIONS AND CLINICAL IMPORTANCE: Decreased vitamin D metabolite concentrations and decreased antimicrobial peptide concentrations suggest that vitamin D has important immunomodulatory functions in newborn foals.