Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/23/2010
Publication Date: 11/29/2010
Citation: Nelson, C.D., Reinhardt, T.A., Beitz, D.C., Lippolis, J.D. 2010. In vivo activation of the intracrine vitamin D pathway in innate immune cells and mammary tissue during a bacterial infection. PLoS One. 5(11):e15469. Available: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0015469. Interpretive Summary: Vitamin D plays an important role in gene regulation in bovine immune cells. Bovine macrophages are cells that ingest pathogens, present antigens for recognition by other immune cells, and produce protein signals that activate other immune cells. We show for the first time that macrophages isolated directly from an infection have genes in the vitamin D pathway activated. This paper highlights the important role of vitamin D in the response to a bacterial infection.
Technical Abstract: The active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), is an important regulator of immune function. The enzyme that synthesizes 1,25(OH)2D3 from 25-hydroxyvitamin D3 is 1alpha-hydroxylase (1alpha-OHase; CYP27B1). Several in vitro studies have shown that TLR signaling induces expression of 1alpha-OHase in monocytes and macrophages. Synthesis of 1,25(OH)2D3 in monocytes and macrophages presumably allows for local control of 1,25(OH)2D3-mediated gene expression. However, induction of 1alpha-OHase expression at the site of an infection has not been shown. Using Streptococcus uberis mastitis in cattle as a model of bacterial infection, we measured 1alpha-OHase gene expression in mammary tissue and cells isolated from the milk during mastitis. In tissue and secreted cells from the infected mammary glands, 1apha-OHase gene expression was much higher compared to expression in tissue and cells from the healthy glands. Separation of the cells by FACS, revealed that 1alpha-OHase was predominantly expressed in the CD14+ cells from the infected gland. Finally, 24-hydroxylase, inducible nitric oxide synthase (iNOS), and RANTES (regulated upon activation, normally T-cell expressed and secreted; CCL5), genes that are upregulated by 1,25(OH)2D3 in cattle, were expressed significantly more in tissue and cells from the infected glands than from the healthy glands. In conclusion, 1alpha-OHase is upregulated in CD14+ cells in an infected mammary gland during mastitis and seems to provide 1,25(OH)2D3 for local regulation of 1,25(OH)2D3-mediated immune responses. To our knowledge, this study provides the first in vivo evidence that 1alpha-OHase expression is upregulated in macrophages in response bacterial infection.