Immune System

Synonyms in the broadest sense

innate immune defence, acquired immune defence, endogenous defence system, antibodies, bone marrow, thymus, spleen, lymph nodes, complement system, monocytes, granulocytes, mast cells, macrophages, killer cells, lymph cells, lymphocytes, B cells, T cells, CD8+ cells, T helper cells, dendritic cells, lymphatic system


The immune system is a system developed over millions of years to protect humans against pathogens such as bacteria, fungi, viruses or parasites (e.g. certain pathogenic worms). Like the human being as a whole, the immune system has also evolved over the course of evolution. A distinction is made between the innate and the acquired immune system. Both parts of the immune system are connected by complex mechanisms, so that a strict separation between the two parts would be difficult and simplistic.


The immune system is a complicated interaction between different organs, such as the thymus, spleen, lymph nodes, appendix, bone marrow and white blood cells. The immune cells of the immune system are formed in these organs or “recruited” to fight against invading pathogens. An enormously important achievement of evolution is the emergence of an immune system “memory“.

This means that invading pathogens can be eliminated more quickly when they enter the body a second time, because the cells “remember” them. The body can initially protect itself against the penetration of pathogenic germs by means of various barriers. An important component of the immune system is (and is often neglected) the skin (incidentally the largest organ in the body).

Because the skin is rather acidic (so-called pH value between 4. 0-6. 5), most viruses, bacteria, fungi and parasites cannot penetrate this barrier.

It is similar to old city walls that protected the inhabitants from attackers. These old city walls often had a certain number of soldiers defending them. The skin also has its own skin germs, which cope well with the acidic environment and also help to destroy intruders.

When pathogens enter the body via the mouth, they eventually reach the stomach acid, which is a very efficient barrier against pathogens. The body/immune system also tries with all its might to free itself mechanically from the pathogens first. In the airways, for example, tiny cilia ensure that intruders are transported to the outside.

By coughing and sneezing, the pathogens are also catapulted out, so to speak. The body therefore initially tries to defend itself in a very unspecific way. Over millions of years, however, a system has developed in which there are special cells for the defense against viruses, bacteria, parasites or even tumor cells. In the following, the innate and the acquired immune defense of the immune system are described.