Vitamin D3 protects turbot (Scophthalmus maximus L.) from bacterial infection.

Accumulating evidence supports that vitamin D3 (VD3) possesses immunomodulatory properties besides its classical actions in calcium and bone homeostasis. In this study, juvenile turbots were fed with the diets containing 0 IU/kg VD3 or the optimum dose of 400 IU/kg VD3 for 8 weeks. To investigate the effects of VD3 on anti-infectious immunity in fish, 107 CFU Edwardsiella tarda was injected intraperitoneally to each juvenile turbot after the feeding trial. Our results showed that the mortality of infected turbots with dietary VD3 was much lower than that in VD3 deficient group, and the supplementation of dietary VD3 significantly reduced the bacterial load in the spleen of infected turbots. Further analysis demonstrated that the production of reactive oxygen species (ROS) in haemocytes and lysozyme activity in serum was elevated, and the responses of T cells and B cells were modulated in VD3-supplemented turbots. Moreover, the inflammation was significantly exacerbated in the infected turbots fed with 0 IU/kg VD3 compared to the fish fed with 400 IU/kg VD3. In addition, the head kidney macrophages (HKMs) in turbots were isolated and incubated with VD3in vitro, the results showed that VD3 significantly promoted the bactericidal activity in HKMs. In conclusion, our study has shown clear evidence that VD3 positively regulates the innate and adaptive immunity in fish, which is beneficial to the defense in fish against pathogen infection.