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The main role of the immune system is to prevent disease caused by infection. Infections can be caused by a wide variety of pathogens, including bacteria, fungi, parasites (such as malaria) and viruses (such as influenza and the common cold). The immune system comprises of a network of cells and tissues that work together to prevent disease. All parts of the body that interact with the external environment (such as the lungs, digestive tract and skin) have to be prepared to protect the body. The skin act
