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Two types of host defense systems
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Innate and adaptive immunity
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First line of defense; nonspecific; always present
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Innate immunity
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Specific or acquired defense
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Adaptive immunity
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Two major classes of lymphocytes in adaptive immunity
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B and T cells
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Lymphocyte most responsible for the clearance of extracellular microbes
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B cells
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Lymphocyte population most responsible for the clearance of intracellular microbes
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T cells
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Classes of T cells
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Helper, cytolytic, regulatory
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Substance, usually foreign, that reacts with an antibody
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Antigen
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Substance, usually foreign that elicits an immune response
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Immunogen
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Lymphocyte population that secretes antibodies
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B cells (plasma cells)
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Lymphocyte population that directly kills infected cells
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Cytotoxic T cells
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Lymphocyte population that helps B cells make antibodies
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T helper cells
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Lymphocyte population that helps activate macrophages
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T helper cells
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Active immunity that is naturally acquired
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Recovery from infection
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Active immunity that is artificially acquired
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Vaccination
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