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Host Defense is a biological concept that refers to the mechanisms used by the immune system to defend the body against pathogens. These mechanisms can be either innate or adaptive, and they work together to protect the body from infection and disease.

Innate Immunity

Innate immunity is the body's first line of defense against pathogens. It includes physical barriers like the skin and mucous membranes, as well as cellular responses like phagocytosis and the release of cytokines. Innate immunity is non-specific, meaning it responds to all pathogens in the same way.

Adaptive Immunity

Adaptive immunity, also known as acquired immunity, is a more specialized form of defense. It involves the production of antibodies by B cells, and the activation of T cells to destroy infected cells. Adaptive immunity is specific to the pathogen that triggered it, and it has the ability to remember previous infections, leading to a faster and stronger response upon re-exposure.

Immune Response

The immune response is the process by which the immune system detects and eliminates pathogens. It begins with the recognition of antigens, which are molecules on the surface of pathogens that are recognized as foreign by the immune system. This triggers a series of events that includes the activation of immune cells, the production of antibodies, and the destruction of infected cells.

Immune System Disorders

Disorders of the immune system can lead to a variety of health problems. These include autoimmune diseases, in which the immune system attacks the body's own cells; immunodeficiency disorders, in which the immune system is not able to mount an effective defense; and hypersensitivity reactions, in which the immune system overreacts to harmless substances.

See Also

• Inflammation
• Immunology
• Vaccination

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