The dairy cow endures a transitional period that spans the 6 weeks surrounding parturition that is both a physically and metabolically demanding life stage. During this stage, the cow has increased susceptibility to an array of inflammatory/infectious diseases. Negative energy balance, subsequent lipid mobilization and increased plasma NEFA concentrations contribute to disease risk and inflammation during this time. Transitioning cows also suffer from a decrease in lipoproteins, including high-density lipoprotein (HDL). HDL has numerous well-documented anti-oxidant and anti-inflammatory properties in a number of species, but its biological activity is understudied in dairy cattle. The current focus of the Behling-Kelly laboratory is investigating the anti-inflammatory properties of bovine HDL and its influence on inflammation and production-related disease in the transitioning cow. We have data that shows HDL can significantly reduce the inflammatory response of bovine endothelial cells to stimulation by TNF-α. However, we do not know the mechanism(s) that underlie this effect. We hypothesize that HDL particles are able to directly bind TNF-α. This would prevent the cytokine from binding to cell surface receptors, thereby neutralizing its ability to induce inflammation. We plan to investigate our hypothesis using two approaches. First, we will use co-immunoprecipitation (Co-IP) to detect physical interaction between TNF-α and HDL ex vivo. Secondly, we will use a proteomic approach to look for bound TNF-α on HDL isolated from cows challenged with lipopolysaccharide (LPS) to induce inflammation in a whole animal system. Unraveling the mechanism(s) by which HDL blunts TNF-α stimulated inflammation will get us one-step closer to understanding the anti-inflammatory properties of HDL in dairy cattle. This is important to the industry, as dietary manipulation can impact lipid metabolism and the physical properties of lipoproteins, including HDL. The current work may promote future investigations that could lead to nutritional or pharmacological interventions to improve the overall health of the dairy cow and the efficiency of milk production for the industry.