AUTHOR=Soto-Dávila Manuel , Valderrama Katherinne , Inkpen Sabrina M. , Hall Jennifer R. , Rise Matthew L. , Santander Javier 

TITLE=Effects of Vitamin D2 (Ergocalciferol) and D3 (Cholecalciferol) on Atlantic Salmon (Salmo salar) Primary Macrophage Immune Response to Aeromonas salmonicida subsp. salmonicida Infection

JOURNAL=Frontiers in Immunology

VOLUME=10

YEAR=2020

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.03011

DOI=10.3389/fimmu.2019.03011

ISSN=1664-3224

ABSTRACT=<p>Vitamin D<sub>2</sub> (ergocalciferol) and vitamin D<sub>3</sub> (cholecalciferol) are fat-soluble secosteroid hormones obtained from plant and animal sources, respectively. Fish incorporates vitamin D<sub>2</sub> and D<sub>3</sub> through the diet. In mammals, vitamin D forms are involved in mineral metabolism, cell growth, tissue differentiation, and antibacterial immune response. Vitamin D is an essential nutrient in aquafeeds for finfish. However, the influence of vitamin D on fish cell immunity has not yet been explored. Here, we examined the effects of vitamin D<sub>2</sub> and vitamin D<sub>3</sub> on <italic>Salmo salar</italic> primary macrophage immune response to <italic>A. salmonicida</italic> subspecies <italic>salmonicida</italic> infection under <italic>in vitro</italic> conditions. We determined that high concentrations of vitamin D<sub>2</sub> (100,000 ng/ml) and D<sub>3</sub> (10,000 ng/ml) affect the growth of <italic>A. salmonicida</italic> and decrease the viability of <italic>S. salar</italic> primary macrophages. In addition, we determined that primary macrophages pre-treated with a biologically relevant concentration of vitamin D<sub>3</sub> for 24 h showed a decrease of <italic>A. salmonicida</italic> infection. In contrast, vitamin D<sub>2</sub> did not influence the antibacterial activity of the <italic>S. salar</italic> macrophages infected with <italic>A. salmonicida</italic>. Vitamin D<sub>2</sub> and D<sub>3</sub> did not influence the expression of canonical genes related to innate immune response. On the other hand, we found that <italic>A. salmonicida</italic> up-regulated the expression of several canonical genes and suppressed the expression of <italic>leukocyte-derived chemotaxin 2</italic> (<italic>lect-2</italic>) gene, involved in neutrophil recruitment. Primary macrophages pre-treated for 24 h with vitamin D<sub>3</sub> counteracted this immune suppression and up-regulated the transcription of <italic>lect-2</italic>. Our results suggest that vitamin D<sub>3</sub> affects <italic>A. salmonicida</italic> attachment to the <italic>S. salar</italic> primary macrophages, and as a consequence, the <italic>A. salmonicida</italic> invasion decreased. Moreover, our study shows that the positive effects of vitamin D<sub>3</sub> on fish cell immunity seem to be related to the <italic>lect-2</italic> innate immunity mechanisms. We did not identify positive effects of vitamin D<sub>2</sub> on fish cell immunity. In conclusion, we determined that the inactive form of vitamin D<sub>3</sub>, cholecalciferol, induced anti-bacterial innate immunity pathways in Atlantic salmon primary macrophages, suggesting that its utilization as a component of a healthy aquafeed diet in Atlantic salmon could enhance the immune response against <italic>A. salmonicida</italic>.</p>