In Vivo Activation of the Intracrine Vitamin D Pathway in Innate Immune Cells and Mammary Tissue during a Bacterial Infection

In Numerous in vitro studies have shown that toll-like receptor signaling induces 25-hydroxyvitamin D-3 1 alpha-hydroxylase (1 alpha-OHase; CYP27B1) expression in macrophages from various species. 1 alpha-OHase is the primary enzyme that converts 25-hydroxyvitamin D-3 to 1,25-dihydroxyvitamin D-3 (1,25(OH) D-2(3)). Subsequently, synthesis of 1,25(OH)(2)D-3 by 1 alpha-OHase in macrophages has been shown to modulate innate immune responses of macrophages. Despite the numerous in vitro studies that have shown 1 alpha-OHase expression is induced in macrophages, however, evidence that 1 alpha-OHase expression is induced by pathogens in vivo is limited. The objective of this study was to evaluate 1 alpha-OHase gene expression in macrophages and mammary tissue during an in vivo bacterial infection with Streptococcus uberis. In tissue and secreted cells from the infected mammary glands, 1 alpha-OHase gene expression was significantly increased compared to expression in tissue and cells from the healthy mammary tissue. Separation of the cells by FACS9 revealed that 1 alpha-OHase was predominantly expressed in the CD14(+) cells isolated from the infected mammary tissue. The 24-hydroxylase gene, a gene that is highly upregulated by 1,25(OH)(2)D-3, was significantly more expressed in tissue and cells from the infected mammary tissue than from the healthy uninfected mammary tissue thus indicating significant local 1,25(OH)(2)D-3 production at the infection site. In conclusion, this study provides the first in vivo evidence that 1 alpha-OHase expression is upregulated in macrophages in response to bacterial infection and that 1 alpha-OHase at the site of infection provides 1,25(OH)(2)D-3 for local regulation of vitamin D responsive genes.