The most important tasks of the immune system can be divided into three areas:
- Fighting a wide range of pathogens
- Detecting and defending against pollutants
- Protection against one’s own altered cells
The body’s own protective barrier:
Our immune system is made up of a variety of cells and organs that are interconnected in a variety of ways. Even before pathogens are able to penetrate the body, the first barrier, the “body's own protective barrier”, must be overcome:
Skin and mucous membranes act as an external, mechanical protective barrier. In addition, pathogens are held back by the skin’s acid mantle. Dust, dirt and pathogens are transported out of the body again by sneezing and coughing.
Bronchial mucus and cilia in the airways also provide a barrier. Regular flushing of the bladder and urethra through the flow of urine, and an acidic environment in the vagina, also provide protection. Enzymes in the saliva, tear fluid and respiratory tract can kill harmful micro-organisms, as can the hydrochloric acid in stomach acid.
Organs of the immune system:
If pathogens manage to penetrate the body despite the mechanical hurdles, the organs of the immune system come into play. These can be divided into primary and secondary lymphatic organs. The lymphatic system controls the production and maturation of immune cells, the lymphocytes.
The bone marrow and the thymus are the primary lymphatic organs in which lymphocytes are formed from the so-called stem cells. From there, the lymphocytes are then passed through the blood to the secondary lymphatic organs, which include the lymph nodes, spleen, tonsils, lungs, mucous membranes and the lymphatic tissue in the gastrointestinal tract.
In the secondary lymphatic organs, the lymphocytes then multiply, continue to mature and specialise. From here, the immune response to a pathogen is initiated.
Through the lymph flow, the immune cells are transported in large quantities to their “place of use” as quickly as possible. Swollen lymph nodes or tonsils are therefore a sure sign that our body is fighting infections – the immune system is working at full speed.
Specific immune response and non-specific immune response
Essentially, our immune system can be divided into two defence mechanisms: the innate (non-specific) immune response and the acquired (specific) immune response, which are linked to one another in many ways.
The innate immune response is directed against all the body’s intruders, while the acquired response works specifically against already known pathogens and has formed special antibodies.
Antibodies are proteins that react to certain substances (antigens). Our immune system therefore makes antibodies when it identifies antigens.
All the body’s defence cells are derived from stem cells, which are formed in the bone marrow and belong to the white blood cells (leukocytes). The stem cells can adopt two different differentiations (“specialisations”):
- They can differentiate into granulocytes, monocytes and macrophages (“phagocytes”), which are part of the non-specific immune system.
- Or they become lymphatic stem cells, from which lymphocytes then develop. Lymphocytes can be divided into subgroups: T cells, B cells and natural killer cells. They are part of the specific immune system.
Innate, non-specific immune system
From birth, our body already has effective and fast defences against infections, inflammation, allergic reactions and autoimmune diseases.
We have the body's own protective barrier, enzymes, messenger substances and white blood cells at our disposal. Leukocytes, or white blood cells, are particularly effective immune cells against pathogens.
Since the innate immune system has no memory, each intruder is attacked in an untargeted manner but within a very short time. For example, bacterial infections can already be stopped by the innate immune system, since the cells known as “phagocytes” (macrophages, monocytes and granulocytes) as well as certain proteins can intervene immediately. Only when the non-specific immune system is unsuccessful does the specific immune system come into play.
Incidentally, the phagocytes also support the immune system by eliminating dead cells in the body. This is how, for example, the emergence of sources of infection can be prevented.
Acquired, specific immune system
The acquired, specific immune response is formed over the years through contact with pathogens and remembers their characteristics. The lymphocytes formed in the bone marrow, which form antibodies after contact with foreign bodies, play a special role here.
When the pathogen attacks again, the body reacts with a targeted immune response thanks to the antibodies. The “immunological memory” is the reason why we are protected from many diseases for years or, at best, only have to suffer them once and then are immune. However, it can take four to seven days for the antigens of the specific defence system to take hold.
Vaccinations – building up antibodies
Immunological memory is used when it comes to vaccinations. Attenuated pathogens are administered via the vaccine, which do not cause disease, but only stimulate the body to form antibodies and memory cells. If a person is vaccinated against a pathogen, the body already knows how to act against the intruder and is immune.
Often, several partial vaccinations have to be carried out for a basic immunisation. Some vaccinations only need to be given once, while others are refreshed at certain intervals. This vaccination procedure is also referred to as “active immunisation”.
In “passive immunisation”, a concentrate of antibodies is injected that comes from humans or animals that are already immune to the pathogen and have formed antibodies. In contrast to active immunisation, passive immunisation offers immediate protection, but only lasts for a few months.