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Communicable diseases, disease prevention and the immune system Typeit
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A is a disease-causing organism. There are many types of microorganisms which can cause disease:
Plants have defences against infection that are always present, such as cellulose cell walls and bark, as well as defences which only take place when damage occurs, such as the deposition of under the cell wall near the site of infection, or the production of chemicals, including bitter that deter herbivores and can modify some enzyme-controlled reactions.
Animals have some non-specific defences against disease, such as the response which causes swelling as a result of histamine release, signalling the site of infection to white blood cells. Non-specific proteins called can also bind antigens, promoting phagocytosis. The antigens may then be partially digested by , which become antigen-presenting cells in order to help other immune cells recognise the antigen and avoid an response (where immune cells attack other non-foreign cells of the body).
Animals also have specific defences, which primarily use antibodies produced by cells. Because antibodies are produced, this is a type of immunity, whereas other types of immunity involve receiving antibodies that are already fully formed. The secondary immune response after a specific pathogen has already been detected by the body is initiated by in the blood, and these act to produce the correct antibodies to defend against the pathogen's antigens. Antibiotics are often used to aid the immune response against bacterial infections; however, because of their overuse and misuse, some strains of bacteria have developed to common antibiotics, meaning they are no longer effective.