Got milk? It’s not just your bones that will thank you!
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For decades now, parents have been telling their children the importance of drinking milk to grow big and strong. Milk is full of nutritious proteins, lipids, calcium, and vitamin D. What our parents didn’t know is that while vitamin D is highly important for skeletal development, it has the incredible capacity to mediate immune responses to bacterial infections!
Recently, the Chen group from The University of Tasmania School of Medicine in Australia published a paper detailing the results of their experiments surrounding how vitamin D is important for the immune response against gram-negative bacteria. Gram-negative bacterial infections are harder to treat with antibiotics as most drugs will not penetrate the lipopolysaccharide coating found on the gram-negative cell wall. The study found that airway epithelial cells required vitamin D to treat upper respiratory bacterial infections.
In these cells, it was found that with vitamin D, white blood cells were able to produce more cytokines and increase their phagocytic ability to destroy pathogens. The authors suggest that the increase in upper respiratory infections during the winter months has to do with the fact that exposure to UV light from the sun is diminished, and vitamin D precursors cannot be converted to the active form. During upper respiratory infections, 1α, 25-Dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, up regulates the productions of these inflammatory cytokines in immune cells as well as in the respiratory epithelial cells themselves.
In order to study these phenomena, the authors conducted in vitro studies. The authors purchased human respiratory epithelial cells and treated some with a control solution of dilute ethanol and some with 1,25(OH)2D3. Both sets of cells were treated with artificial lipopolysaccharide. They used ELISA to quantify the amount of cytokine produced in the supernatant by the epithelial cells and found that the cells treated with vitamin D produced a statistically significant higher amount of cytokines They repeated the process with neutrophils and monocytes that were isolated from freshly drawn human blood and assessed the inflammatory activity of these cells with the same ELISA quantification method and noted similar results to the epithelial cells
To assess the phagocytic abilities of cells that had been treated with vitamin D, the authors incubated neutrophils and monocytes that had been treated with 1,25(OH)2D3 and the control, ethanol, with fluorescent E. coli. The incubation period was allowed to go on for an hour and then was stopped with ice. The level of fluorescence inside the cells was assessed with flow cytometry. Cells that had been treated with 1,25(OH)2D3 not only phagocytosed more of the E. coli, but were able to produce more and different types of cytokines than those that were not treated with 1,25(OH)2D3.
The implications of this study are numerous. This study is likely to trigger changes to treatment protocol of gram-negative bacterial infections to include vitamin D supplementation along with antibiotic treatment. Outside of hospitals, people might consider supplementing their own diet with foods rich in vitamin D as well as with vitamin D pills. Our BCM 441 class discussed how vitamin D research in the field of immunology is a relatively new project that has developed in the last 10 years. Continuing to examine how vitamin D supplementation can boost the immune system will be incredibly important in the battle against antibiotic resistance and the treatment of gram-negative infections.
Chen, L., Eapen, M. S., and Zosky, G. R. (2017) Vitamin D both facilitates and attenuates the cellular response to lipopolysaccharide. Sci. Rep. 7, 45172
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