immune system

The immune system protects the body from invaders and pollutants. To do this, it makes use of various defense mechanisms. How do the immune system work? What is part of the immune system? How can you strengthen the immune system? You can find out all of this here!

What is the immune system?

The immune system is the human defense system against foreign substances and germs. This is important because the body is in constant contact with its environment. And there are a multitude of bacteria, viruses, fungi and parasites there. If they penetrate the body, they can be life-threatening in some cases Infections cause.

But pollutants - for example from the air - can also damage the body. The job of the immune system is to prevent infection, fight unwanted invaders and eliminate toxic substances. The defense system comprises several organs, different cells and proteins.

How is the immune system built up?

The structure of the immune system is complex. It consists of numerous components. The immune system can only protect the body from pathogens and co. Only if all components work together correctly.

Organs of the immune system

In addition to the blood, the organs of the immune system include the so-called lymphatic system with the lymphatic organs. In addition, the skin and mucous membranes offer important protection against substances and intruders from the outside.

Skin and mucous membranes

All over the body, the skin and mucous membranes are the first important barriers against bacteria, viruses and fungi, for example. They are like a mechanical protective wall that shields the body from the outside.

There are other defense mechanisms that support the immune system:

Bacteria-inhibiting substances (e.g. enzymes in saliva, urine or tear fluid) stop foreign intruders.
In the respiratory tract, mucus ensures that inhaled pollutants initially stick and are transported outwards again by the movement of the cilia.
Stomach acid destroys most of the pathogens that enter the body through food.
Useful microorganisms colonize the skin and many mucous membranes (e.g. the microbiome of the intestinal flora) and fight off pathogens.
Reflexes (coughing, sneezing) also protect against pathogens.

Primary lymphatic organs

The lymphatic system consists of the lymph vessels and the primary and secondary lymphatic organs. The primary lymphatic organs form certain defense cells, the lymphocytes. These organs include:

Bone marrow: central organ of the immune system inside the bones in which the blood cells are formed and, for the most part, also mature - with the exception of immature T lymphocytes
thymus: Organ above the pericardium in which the T precursor cells mature

Secondary lymphatic organs

In contrast to the primary lymphatic organs, an actual immune defense takes place in the secondary ones. The mature immune cells migrate from their place of formation to where they then develop further, depending on the pathogen and pollutant, and ward off the intruders. These organs of the immune system include:

spleen: Foreign substances (antigens) reach the organ in the left upper abdomen via the blood
Lymph nodes: As a rule, antigens get there via the lymph from the lymph vessels
Mucosa-associated lymphatic tissue (MALT): The surface of the tissue creates contact between foreign substances and immune cells, which then take up the fight.
- Almonds (Tonsils, NALT = Nasal-Pharyngeal-Associated Lymphoid Tissue), e.g. tonsils or tonsils
- Gut-Associated Lymphoid Tissue (GALT), such as appendix and the Peyer's plaques im Small intestine
- Immune tissue in the airways (BALT = Bronchus-Associated Lymphoid Tissue)
- Lymphatic tissue in the urinary tract

Thymus - training camp for immune cells Immune cells are shaped in the thymus gland - but only in the first years of life. Find out here why the thymus is no longer active in adults. Learn more

The spleen (Splen, Lien) is the largest lymphatic organ in the body. Read more about their location and anatomy as well as important spleen diseases! Learn more

Immune cells

Numerous cells are involved in the immune system. They are called white blood cells, medicinally Leukocytes. The various cells of the immune system communicate with one another either directly via special surface markers or via soluble messenger substances such as so-called cytokines.

Granulocytes

Granulocytes are part of the first wave of defense. About 40 to 60 percent of leukocytes are granulocytes. Among other things, they swim in the blood, but they can also leave the bloodstream and migrate into the tissue. The granulocytes are part of the unspecific immune system. Doctors differentiate:

Neutrophils: Mainly absorption and killing of pathogens, used granulocytes form the basis for pus
Eosinophils: esp. killing of parasites and viruses, involved in allergic reactions
Basophils: mainly participate in allergic processes, fight harmful substances, especially parasites

Lymphocytes

the Lymphocytes play an important role in the acquired, specific defense. They also form the so-called immune memory, the basis for the ongoing protection of vaccinations. Experts divide the lymphocytes into:

B cells (B lymphocytes)
B cells are created in the bone marrow. This is where the name B cells comes from - from "bone marrow". From there they migrate to lymphatic tissue, where they are activated. They then encounter foreign substances there and in the blood. As mature plasma cells, they produce antibodies. These in turn initiate the destruction of the intruder in various ways.

T cells (T lymphocytes)
T cells are white blood cells that are involved in the immune system. The T cells are created in the bone marrow and then migrate to the thymus (hence the T). This is where the immune cells mature before they, like the B cells, circulate between lymphoid tissue and blood. There are two main types:

T helper cells, also known as CD4 + T cells, activate the B lymphocytes via messenger substances and thus set the specific defense in motion. They also include the regulatory T cells, which help to prevent or end excessive immune reactions.
Killer T cells are also known as CD8 + T cells or cytotoxic T lymphocytes. They recognize cells or tumor cells infected by viruses and destroy them.

B memory cells / T memory cells
Some of both the B and T lymphocytes develop into memory cells after the first contact with the pathogen. If the same pathogen penetrates the body again at a later point in time, the specific immune system "remembers" it. This immune memory enables it to react faster and set the appropriate immune response in motion.

This principle is also used for vaccinations. The usually harmless vaccine mimics the first contact with the pathogen. Thereupon specific antibodies and the immunological memory develop. If the immune system then encounters the "real" germ in the future, it can be fended off quickly and effectively.

NK cells

Some scientists regard the NK cells as a subtype of lymphocytes, others as a separate cell series. In contrast to B and T lymphocytes, they cannot recognize specific antigens. In addition, the NK cells are immediately ready for defense. That is why they are part of the unspecific immune system. They recognize and kill virus-infected and malignant cells.

Monocytes

Monocytes are very large white blood cells. They also come from the bone marrow and can swim freely in the blood. Or they develop into so-called macrophages when they leave the bloodstream and migrate into the tissue.

As part of their defense work, the monocytes or macrophages "devour" bacteria and other microorganisms, cell debris and other particles (phagocytosis) in order to dissolve or store them. This group is therefore also called phagocytes.

Not only do they "eat", they also attract other immune cells via messenger substances. They also present parts of the entangled pathogens to the specific lymphocytes (antigen presentation). In addition, they play a decisive role in inflammatory reactions (cytokine release) and activate the complement system.

Dendritic cells

In order for lymphocytes to develop and become active, they need contact with antigens. Only some B cells can recognize this directly. T lymphocytes, on the other hand, need other cells for this. These are the so-called antigen-presenting cells.

In addition to macrophages and B-lymphocytes, so-called dendritic cells are also included. They have their origin in the bone marrow and are located in a wide variety of tissue types, for example in the skin. There they "wait" with their long cell extensions for foreign substances, which they can absorb, process and present as foreign antigens on their own surface.

Leukocytes: This is what the white blood cells do. Leukocytes are cells in the blood that are responsible for defense against infection. Without them, the immune defense does not work. Read all about it! Learn more

Humourous defense

Doctors call the fight against pathogens using defense cells cellular immune defense. There are also so-called humoral mechanisms. They are based on special proteins. These can fight intruders directly. In addition, they initiate further immune reactions and strengthen them. The humoral immune response is part of the innate defense system.

Complement system

The so-called complement system is a defense mechanism that belongs to the innate immune system. It consists of different proteins, the complement factors. These come from the liver and float around in the blood. You have three important tasks:

Direct defense: The complement system can destroy pathogens directly.
Mark the pathogen: The complement factors can mark intruders (opsonization). Scavenger cells can then recognize and devour the germs more easily (phagocytosis).
Increased inflammation: The proteins attract additional immune cells and make the blood vessels more permeable - one reason why inflamed tissue swells.

Acute phase proteins

Macrophages and dendritic cells release certain messenger substances (cytokines) during the first defense against pathogens. As a result, they not only attract other immune cells. They also trigger what is known as the acute phase reaction in the liver. The liver cells then produce more specific proteins.

Among other things, these acute phase proteins mark pathogens so that scavenger cells can better recognize and absorb them. Some of the proteins can also activate the complement system.

In addition to the immune cells, doctors can also determine acute phase proteins in the blood. Well-known representatives are Ferritin and the C-reactive protein (CRP).

Immune system cytokines

These proteins are special messenger substances. They are produced by immune cells. Well-known cytokines (cytokines) are interleukins, interferons or tumor necrosis factors (e.g. TNF-alpha). They have a wide variety of functions. As chemokines, for example, they attract other immune cells. In addition, they regulate the reproduction of immune cells and control their further development.

How does the immune system work?

The work of the immune system begins as soon as a pathogen has penetrated the organism, for example in the case of a minor skin injury.

Nonspecific immune defense

The unspecific immune system is already present at birth. It is therefore also called the natural or innate immune system. As the first instance in a defensive battle, it can react quickly to foreign substances.

However, it can hardly distinguish between the different intruders. Therefore, the unspecific immune defense is often not sufficiently effective and only able to prevent the spread of some pathogens in the body to a limited extent.

Various components belong to the system of unspecific defense:

Skin and mucous membranes
Body fluids (e.g. saliva, mucus, urine, stomach acid)
Local protective mechanisms (e.g. cilia)
Natural flora (e.g. bacteria in the intestines or on the skin)
Defense cells (e.g. monocytes, granulocytes, NK cells)
Proteins (e.g. acute phase proteins, cytokines, complement factors)

Specific immune defense

Since the unspecific defense system is often insufficient, the specific immune defense is so important, also known as the adaptive or acquired immune system. It is mainly brought about by the antigen-presenting cells. The specific defense cells can then take targeted action against certain pathogens.

In order to develop enough clout, the acquired immune defense needs time, often hours and days. To do this, it also trains the so-called immune memory: If the same pathogen is infected again, the immune system can react more quickly.

In the specific immune system, different immune cells and tissues work together to fight off pathogens and foreign substances. This includes:

T cells
B cells (as plasma cells, antibody production)

Course of the immune response

In order for the immune system to react to an intruder, it must first be recognized.

Phase 1: First response to intrusion

Once a pollutant or germ has overcome the first barriers, it penetrates the body. This can happen, for example, through a skin injury. This stimulus first calls cells of the unspecific immune defense, such as macrophages and granulocytes, on the scene.

Phase 2: "Examine" foreign substances and combat them

Every foreign substance or pathogen has characteristics, for example proteins, carbohydrates and fats, on its surface that the body recognizes as foreign. The unspecific defense cells react to special "patterns" on the surface of the foreign matter, so-called Pathogen Associated Molecular Patterns, or PAMPs for short.

Then they pour out various substances. These can, for example, destroy the pathogen directly. Other substances increase the function of the immune cells or induce new ones.

Phase 3: Identifying specific pathogens

The so-called antigens are much more specific than the PAMPs. The foreign antigens are mostly proteins, but can also consist of fat or sugar molecules. A PAMP basically consists of several antigens. These mobilize the specific defense cells that can target individual pathogens.

B cells can either bind directly to the appropriate antigens or they bind to antigen-presenting cells (APC). T lymphocytes always need the help of APZ. In both cases, the principle works like a lock that only fits a certain key.

Phase 4a: T cells become active

As soon as the T lymphocytes are docked on the appropriate antigen, they become active. Messenger substances, the cytokines, stimulate the T cells to divide, among other things. In this way, only the T cells that match the pathogen multiply. The immune response is thus “tailor-made”.

Phase 4b: B cells position themselves

The situation is similar with the B lymphocytes. When they have bound to antigens, they in turn present these themselves on their surface. This is where T helper cells come into play: once they have docked there, they use messenger substances to give the B cells the signal to multiply.

This creates two types of B cells. The B memory cells for protection against new, future diseases caused by the same pathogen and the plasma cells.

Phase 5: antibody production

The plasma cells produce matching antibodies, too Immunoglobulins called. These are special proteins for immune defense. Each intruder gets "own" antibodies.

Phase 6: The antibodies work

The antibodies bind firmly to the pathogen's antigen, for example to components of the shell of bacteria or viruses. This has several advantages:

Opsonization: Antibodies "mark" the pathogen for other immune cells. Phagocytes, for example, recognize the intruders more easily, which are riddled with antibodies all around.
Neutralization: Antibodies can, for example, neutralize the toxins of invading germs. If the immunoglobulins bind to viruses, they prevent the viruses from penetrating human cells. As a result, these can no longer multiply.
Complement activation: The antigen-antibody complexes also activate the complement system. This leads to the destruction of the pathogens or infected cells. The complement system also attracts additional defense cells and marks pathogens. It connects the unspecific with the specific immune system.

Weak immune system

In some cases the immune system is no longer as powerful and the body is more susceptible to infections. There are numerous factors that can cause weak immune systems. In many cases, lifestyle plays a role. This can usually be changed in a positive way. In some cases, however, there is a disease behind it.

Causes of a Weak Immune System

Reasons for a weakened immune system are, for example:

Old age
stress (physical and mental)
Unhealthy resp. Malnutrition
Lack of sleep and sleep disorders
Sedentary lifestyle
smoking and alcohol
Existing infections and inflammations
Blood cancer and immunodeficiency
Chronic diseases (e.g. Diabetes mellitus, COPD, HIV / AIDS)
Autoimmune diseases (e.g. inflammatoryrheumatism)
Immune-suppressing drugs (immunosuppressants), chemotherapy, Irradiation

Signs of a weak immune system

If the defense is weakened, intruders have an easier time. Pathogens can more easily penetrate the body, multiply and spread there. The result: you get sick more often.

In addition to this susceptibility to infection, a weakened immune system often leads to general symptoms. These include, for example:

fatigue and exhaustion
Long-lasting course of the disease
Increasedallergic reaction
Hair loss
Skin irritation

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What are autoimmune diseases?

In an autoimmune disease, the immune system is directed against healthy, endogenous tissue. Autoimmune diseases can attack any tissue and also organs.

Autoimmune diseases You can find out what autoimmune diseases there are, what symptoms they have and how they are treated in the topic special. Learn more

How can you strengthen the immune system?

Above all, a healthy lifestyle contributes enormously to the fact that the immune system works reliably. You can naturally strengthen your immune system through regular exercise alone. A balanced diet is also an important cornerstone. As a rule, it provides the body with all the important components that are necessary for the immune system to run smoothly.

This includes, above all, vitamins like thatVitamins A, B6, B9 (Folic acid), C. andE. as well as minerals and trace elements such asselenium orzinc. But also Vaccinations basically strengthen the natural defenses. They set off defense reactions that also take place in the fight against real pathogens: the immune system forms specific antibodies and memory cells. The vaccination "trains" the immune system, so to speak, for an emergency.

Herbal remedies can additionally support immune work.homeopathy should also be able to strengthen the immune system. Their specific effectiveness is controversial in science and not clearly proven by studies.Other tips for a healthy immune system are: relax, sleep well and drink enough water.

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Immune system in children

There are clear differences between the immune system in children and in adults. Nevertheless, newborns already have all the important basic immune systems. From then on, the immune system continues to develop - for example by encountering new pathogens.

Children, especially when they go to daycare or kindergarten, feel permanently ill. Numerous germs change back and forth due to the close contact between the playing children. Nevertheless, parents should not wrap their children in cotton wool: this is the only way for the immune system to "learn" and develop an immune memory.

Regardless of this, you can strengthen your child's natural defenses. For example, make sure you have a healthy diet right from the start. And motivate your children to go and exercise in the fresh air.

Immune system in children How can you strengthen the immune system in children? How does it differ from the adult body defense? Read more about it here! Learn more