Immune Response Definition

The multiple mechanisms and processes through which the body identifies and reacts to antigens. The immune response is the body’s primary means of protecting itself from infection. There are three independent yet complementary immune response pathways: Antibodymediated immunity (also called humoral immunity), cell-mediated immunity, and the complement cascade. As well, the immune response stimulates activity from the nervous system and the endocrine system.

The immune response relies largely on antibodyantigen binding. Antigens are molecules that identify cells to the immune system. Antibodies are molecules the immune system produces to bind with nonself antigens-antigens on cells that do not belong to the body. With antibody-antigen binding, the antibody releases proteins called opsonins that mark the antigen-bearing cell for destruction by killer T-cells and natural killer (NK) cells.

Monocytes (in the blood circulation) and macrophages (in the tissues) consume the cellular debris remaining after the marked cell’s destruction. Antibody-antigen binding also activates the complement cascade, a biochemical response that produces proteins that attach to and damage the cell membrane of cells that the immune response identifies as nonself.

Key Feature of The Immune Response

A key feature of the immune response is inflammation, the process by which the body increases the ability of plasma, the liquid component of blood, to seep into the tissues (interstitial spaces). Histamine and prostaglandins are the primary agents of the inflammatory response.

Inflammation floods the tissues with immune molecules to extend the immune response beyond the blood and the lymph. Inflammation also serves to contain the infection, keeping it from spreading beyond its point of origin to other areas of the body.

For further discussion of the immune response within the context of the structures and functions of the immune system, please see the overview section “The Immune System and Allergies.”


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