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Immune system

from Latin: immunis - untouched
Synonyms: Immune defense, defense system
German: Immunsystem

1 Definition

The immune system is the defense system of biological organisms against foreign substances or living creatures. It differs between the body's own and foreign structures, and it thereby serves the maintenance of individual integrity. Not only humans and animals have an immune system, but also plants and - in a strongly reduced manner - even microorganisms.

2 Background

The complexity of an immune system increases with the phylogenetic stage of development of a bioorganism: The more complex the structure to be protected is, the more manifold is the immune system. In humans, the immune system consists of specialized proteins (antibodies), immune cells and immune organs. It is the carrier of the immune response of our body.

Bacteria, viruses, fungi, and protozoan or multicellular parasites are the typical germs that the immune system reacts to.

3 Components

The human immune system is constructed of several components. One can differentiate between a cellular and a humoral part.

3.1 Cellular immune system

The cellular immune system comprises specialized immune cells that either are mobile (eg. in the blood) or sessile in the different tissues. These include:

3.2 Humoral immune system

The humoral immune system is the part of the immune system that is not based on cells, but on plasma proteins. They comprise:

3.3 Surface barriers

In the wider sense of the word, the skin and the mucosa are also parts of the immune system, since, with their barrier function, they prevent the uncontrolled invasion of antigens into the tissues of the body. They grant this barrier function with an especially close, almost seamless cell association that is additionally reinforced by collagens.

Skin and mucosa do not only provide mechanical protection, but also defend the body with surface secretions that contain chemical defensive substances such as antimicrobial peptides, immunoglobin A, lysozymes and defensins. In the gastrointestinal tract and in parts of the urogenital tract, they maintain a saprophytic bacterial flora that holds the pathogenic germs at bay.

4 Classification

The response of the immune system to antigens is called immune response. This immune response can be classified according to several aspects:

4.1 ...according to the involved components

4.2 ...according to specificity

4.3 ...according to contact history

4.4 ...according to developmental stage

Also, the immunotolerance is a form of the immune response.

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