Immune response

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Immune response

Immune system structures

Definition

The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful to the body.

Alternative Names

Innate immunity; Humoral immunity; Cellular immunity; Immunity; Inflammatory response; Acquired (adaptive) immunity

Information

The immune system protects the body from potentially harmful substances by recognizing and responding to antigens. Antigens are molecules (usually proteins) on the surface of cells, viruses, fungi, or bacteria. Nonliving substances such as toxins, chemicals, drugs, and foreign particles (such as a splinter) can be antigens. The immune system recognizes and destroys substances that contain these antigens.

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Even your own body cells have proteins that are antigens. These include a group of antigens called HLA antigens. Your immune system learns to see these antigens as normal and does not usually react against them.

INNATE IMMUNITY

Innate, or nonspecific, immunity is a defense system that you are born with. It protects you against all antigens. Innate immunity involves barriers that keep harmful materials from entering your body. These barriers form the first line of defense in the immune response. Examples of anatomical innate immunity include:

Cough reflex
Enzymes in tears and skin oils
Mucus, which traps bacteria and small particles
Skin
Stomach acid

Innate immunity also comes in a protein chemical form, called innate humoral immunity. Examples include: the body's complement system and substances called interferon and interleukin-1 (which causes fever).

If an antigen gets past these barriers, it is attacked and destroyed by other parts of the immune system.

ACQUIRED IMMUNITY

Acquired immunity is immunity that develops with exposure to various antigens. Your immune system builds a defense that is specific to that antigen.

PASSIVE IMMUNITY

Passive immunity involves antibodies that are produced in a body other than your own. Infants have passive immunity because they are born with antibodies that are transferred through the placenta from the mother. These antibodies disappear between 6 and 12 months of age.