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8 Immunity: defenceagainst disease
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Immunity
• Infection is entry into the body of a micro-organism that may cause disease. Infection does not necessarily lead to disease.
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• The immune system has two kinds of response to the entry of foreign material. One response involves natural or innate immunity, which is non-specific.
• The other response involves acquired or adaptive immunity, which is highly specific. Specific immunity involves the production of specialised cells and chemical substances known as antibodies which act against a particular infection.
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Non-specific immunity
• The defence system of the body is called the immune system.
• The immune system is able to identify ‘non-self’ material from ‘self’.
• The immune system can produce two kinds of response to invading foreign material, namely non-specific and specific.
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Non-specific immunity
• Micro-organisms are prevented from entering the body by a number of non-specialised features. This is the first line of defence.
• There is a second line of defence against foreign material that enters the body.
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Specific immunity
• If non-specialised defences fail to prevent infection, specialised responses occur.
• All cells have protein markers on their surfaces.
• Non-self markers on cells entering a person are called antigens.
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Specific immunity
• A number of different kinds of cell are involved in specific immunity.
• The phenotype is the physical, biochemical or physiological expression of the genotype.
• Some cells produce antibodies that circulate in body fluids and react with specific antigens.
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Different kinds of antibodies
• The immune response produces different kinds of T cells.
• Different kinds of T cells have different functions.
• The immune system contains many lymphoid organs and tissues.
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Acquiring specific immunity
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Acquiring specific immunity
• Specific immunity can be acquired in different ways.
• In actively acquired immunity, the immune system of a person produces antibodies in response to antigens.
• In passively acquired immunity, a person receives antibodies from an outside source.
• Both active and passive immunity can be acquired naturally or artificially.
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Adverse events associatedwith immunity
• Any part of the immune response can be faulty.
• Cells of the immune system are involved in allergic reactions.
• An immune system can lose the ability to distinguish ‘self’ from ‘non-self’.
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Adverse events associatedwith immunity
• The action of the immune system can be reduced by treatment with certain drugs.
• Antibodies are sometimes injected to inhibit an immune response.
• Most plants resist infection by mechanical and chemical means