Immunity and Human Immune System

What is Immunity and Definition

An established base of protection against INFECTION. Immunity may be innate, passive, or acquired. INNATE IMMUNITY, also called natural immunity, is present at birth and provides effective protection against a broad base of common pathogens. Innate immunity is limited in scope. PASSIVE IMMUNITY is ANTIBODY-specific but present without activation of the IMMUNE RESPONSE. A newborn has passive immunity based on the antibodies present in his or her mother’s BLOOD. BLOOD TRANSFUSION, PLASMA transfusion, and administration of GAMMAGLOBULIN also convey passive immunity to the recipient. Passive immunity is short term. The body develops acquired immunity through exposure to antigens via infection or vaccination. Acquired immunity is ANTIGEN-specific and long term, often lifelong.

For further discussion of immunity within the context of the structures and functions of the IMMUNE SYSTEM, please see the overview section “The Immune System and Allergies.”

See also ANTIBODY-MEDIATED IMMUNITY; CELL-MEDIATED IMMUNITY; PATHOGEN; VACCINE.

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