A commercial immune modulating feed additive restores L-selectin and CCL5 expression following dexamethasone treatment of murine immune cells in a MyD88-dependent manner.

ABSTRACT

Bovine mastitis costs the dairy industry billions of dollars every year and presents a health challenge in dairy facilities. Immunosuppressive effects of the periparturient period increase the incidence of mastitis. During this time, cattle experience an elevation in circulating cortisol, which reduces polymorphonuclear cell function and ability to clear infection. OmniGen-AF (OMN; Phibro Animal Health, Teaneck, NJ) is an immunomodulatory feed additive that alters gene expression and is used to reduce rates of mastitis. We hypothesized that OMN restores gene expression during periods of immune stress through inhibiting the suppressive effects of glucocorticoid receptor signaling on Toll-like receptor signaling. To test our hypothesis, wild-type (WT) or MyD88 knockout mice were supplemented with OMN and challenged with lipopolysaccharide following dexamethasone (Dex) treatment. Polymorphonuclear cell and macrophage RNA was isolated from intraperitoneal lavages and analyzed for gene expression profiles. Treatment of mice with Dex suppressed expression of l-selectin and CCL5 as compared with phosphate-buffered saline treatment of WT mice. Expression of l-selectin and CCL5 was significantly reduced with Dex treatment in control-fed but not OMN-supplemented WT mice. The protective effect of OMN supplementation on l-selectin expression during Dex treatment was abolished in MyD88 knockout mice. These results suggest that OMN supplementation restores responses of certain genes suppressed by Dex in immune cells in a MyD88-dependent manner. Future research will determine the specific Toll-like receptors, transcription factors, and biochemical properties of OMN that restore gene expression in immunosuppressed cells.