Effects of calcitriol on oxidative burst, phagocytic function, and leukocyte cytokine production in shelter dogs

BACKGROUND: The active metabolite of vitamin D, calcitriol, has been shown across many different species to augment innate immune responses and dampen aberrant proinflammatory cytokine production. Community acquired infections are common in shelters and consume limited shelter resources, impact adoption rates, and can result in unnecessary euthanasia. Prophylactic oral vitamin D supplementation decreases the incidence and severity of upper and lower respiratory tract infections in humans. Before a clinical trial investigating the clinical benefit of oral vitamin D supplementation in shelter dogs can be pursued, an in vitro study evaluating the immunomodulatory effects of calcitriol in blood from shelter dogs is warranted. Therefore, the objective of this study was to determine if incubation of whole blood obtained from apparently healthy dogs housed in a shelter for ≥7 days with calcitriol would alter granulocyte/monocyte (GM) oxidative burst and phagocytic function as well as pathogen-associated molecular pattern (PAMP)-stimulated leukocyte production of tumor necrosis factor (TNF)-α, and interleukin (IL)-6, and IL-10. RESULTS: Ten dogs housed in a shelter for ≥7 days were enrolled in a prospective cohort study. Whole blood from these dogs was incubated with calcitriol (10(− 7) M) or diluent (control) for 24 h. Subsequent to this incubation, phagocytosis of opsonized-Escherichia coli (E. coli) and E. coli-induced oxidative burst were evaluated via flow cytometry. In addition, leukocyte production of TNF-α, IL-6, and IL-10 were measured using a canine-specific multiplex bead assay. Calcitriol significantly decreased leukocyte TNF-α production (p = 0.009) and increased IL-10 production (p = 0.002). Tumor necrosis factor-α-to-IL-10 ratio was significantly decreased with calcitriol (p = 0.017), while IL-6 production as well as GM oxidative burst and phagocytic function were not significantly affected. CONCLUSIONS: These data indicate that calcitriol attenuates proinflammatory immune responses without affecting GM oxidative burst or phagocytic function in vitro in whole blood obtained from apparently healthy shelter dogs.