The immune system has three main functions. First, it scavenges dead or dying cells second, it destroys abnormal cells and lastly, it protects the body from things like pathogens and foreign molecules. The immune system contains three different lines of defense, the physical/chemical barriers, nonspecific resistance and lastly specific resistance. The first barrier is composed of physical and chemical barriers such as the skin, mucous membranes, saliva, tears and even gastric juices. The second line of defense is composed of nonspecific resistance that destroys invaders in a generalized way and it doesn't target specific pathogens, this includes fevers, inflamations and phagocytic cells which ingest and destroy all microbes that pass into the body tissue. Lastly, there is the specific resistance which is the third line of defense, the system uses antigens to identify pathogens and microbes.