Immune System

The immune system is the body's own defence system against higher organisms, which distinguishes between its own and foreign structures and protects the organism against diseases. The immune system (from the Latin immunis actually "tax-free", in the figurative sense untouched, free, pure) is the biological defence system of higher organisms, which prevents tissue damage by pathogens. It removes microorganisms that have penetrated the body, foreign substances and is also able to destroy the body's own cell that have become defective. The immune system is a complex network of different organ, cell types and molecules.

The immune system is of great importance for the physical integrity of living beings, because practically all organisms are constantly exposed to the influences of the living environment; some of these influences pose a threat: If harmful microorganisms enter the body, this can lead to dysfunctions and diseases. Typical pathogens are: bacteria, and fungi, as well as unicellular (e.g. protozoa such as plasmodia) or multicellular parasites (e.g. tapeworms). Changes inside the body can also threaten the existence of a living being: If normal body cells lose their healthy function over time, they usually die and have to be degraded (necrosis) or degrade themselves (apoptosis). In rare cases they can also degenerate pathologically and lead to the development of cancer.

All living beings - whether animals, plants or humans - therefore have protective functions. Even simple organisms possess such a defence mechanism, the so-called innate immune defence; it originated very early in the tribal history of living beings and has remained largely unchanged ever since. The vertebrates also developed a complex, adaptable, so-called adaptive immune defence that protects them even more effectively against pathogens. The plant defence against pathogens is based on completely different mechanisms.

https://de.wikipedia.org/wiki/Immunsystem _{(Wikipedia CC-by-sa-3.0)}