Animation of the mechanism of the toll_like receptor immune response. The blood contains circulating white blood cells, which bear Toll_like receptors green on their surface. These are receptors that are specialised to detect a specific molecule called a lipopolysaccharide or LPS, purple, which is found in the cells walls of pathogenic bacteria yellow. When the receptors binds to the LPS, the cell releases large amounts of cytokines red. The cytokines are hormone_like proteins that act to attract macrophages. Macrophages are white blood cells that engulf and destroy pathogens, helping to prevent serious infection. The 2011 Nobel Prize for Physiology or Medicine was jointly awarded to Bruce Beutler and Jules A Hoffman for their work on identifying the mammalian toll_like receptor.