Corpus: Immune system

The immune system is the defence system of biological organisms against foreign substances or living beings. It distinguishes between its own and foreign structures and thus serves to maintain individual integrity. Not only humans and animals have an immune system, but also plants and - in a greatly reduced form - even microorganisms.

The complexity of an immune system increases with the phylogenetic developmental stage of a bioorganism: the more complex the structure to be protected, the more multi-layered the immune system. In humans, the immune system consists of specialised proteins (antibodies), immune cells and immune organs. It is the carrier of our body's immune response.

Bacteria, viruses, fungi and unicellular or multicellular parasites are the typical pathogens to which the immune system reacts. In addition, the psyche also modulates the activity of the immune system. Chronic stress, for example, is considered a psychogenic immune suppressor.

The human immune system is made up of several components. A distinction is made between a cellular and a humoral part.

Cellular immune system[Bearbeiten]

The cellular immune system includes specialised immune cells that are either freely mobile (e.g. in the blood) or localised in the various tissues. These include:

• Granulocytes
• Macrophages
• Dendritic cells
• Natural killer cells
• T lymphocytes
  • T helper cells
  • Regulatory T cells
  • Cytotoxic T cells
• B lymphocytes

Humoral immune system[Bearbeiten]

The humoral immune system is the part of the immune system that is not based on cells but on plasma proteins. These include:

• Antibodies
• Complement factors
• Interleukins

Surface barriers[Bearbeiten]

In a broader sense, the skin and mucous membranes are also part of the immune system, as their barrier function prevents the uncontrolled penetration of antigens into the body tissues. They ensure this barrier function through a particularly tight, almost gapless cell network, which is additionally reinforced by collagens.

However, the skin and mucous membranes not only provide mechanical protection, but also defend the body with surface secretions containing chemical defence substances such as antimicrobial peptides, immunoglobulin A, lysozymes and defensins. In the gastrointestinal tract and parts of the urogenital tract, they also maintain a saprophytic bacterial flora that keeps pathogens at bay.

The response of the immune system to antigens is known as an immune reaction. This immune response can be categorised according to several aspects:

...by components involved[Bearbeiten]

• cellular immune response
• humoral immune reaction

...according to specificity[Bearbeiten]

• non-specific immune reaction
• specific immune reaction

...according to contact history[Bearbeiten]

• primary immune reaction
• secondary immune response

...according to time of development[Bearbeiten]

• innate immune response
• adaptive immune response

Immune tolerance is also a form of immune response.