1. Skin and mucous membranes Ciliated cells in the respiratory track Bacteria in various places Oil from oil glands Lysozyme from mucous membranes Stomach acid Keep pathogens from entering cells!

2. Inflammatory response Histamines act on capillaries—making them dilate and become permeable Blood flowing to the area makes the area look red and feel hot Fluid leaks from the now more permeable vessels and causes swelling—which causes pain Some WBCs leave the blood and phagocytize pathogens Blood clots can form This response draws attention to the injury (pain), And helps immobolize the site of the injury (swelling) And helps prevent the entry of pathogens (blood clots and phagocytes)

3. Phagocytes and natural killer cells Macrophages act as phagocytes and eat pathogens. Natural killer cells kill host cells that have been infected with viruses NK can also produce cytokines that promote response Pathogens are actually destroyed by these cells Protective proteins Complement = a series of plasma proteins that increase The inflammatory response by increasing histamine release Attracts phagocytes to the injury binding to the pathogen to Attract the phagocyte or poke holes in some pathogens Interferons = proteins released by cells infected by viruses Help protect surrounding cells from being attacked by the Same virus