Lipid metabolism is extensively regulated during the host response to infection. As with other aspects of the host response, these events are mediated by cytokines, including tumor necrosis factor, interleukin 1 (IL-1), IL-6, and the interferons. Cytokines can decrease lipoprotein lipase and increase lipolysis in cultured fat cells. In vivo, many cytokines increase serum triglycerides by increasing very-low-density lipoprotein production. Interferons increase triglycerides predominantly by decreasing lipoprotein lipase activity and triglyceride clearance. These changes in lipid metabolism do not cause cachexia. Rather, they represent part of the host defense, as lipoproteins scavenge infectious particles such as endotoxin.