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The protective shield of our body

The body is in constant exchange with the environment. If the germs in it penetrate the human system, an infection can occur. How this takes place and what strategies can help us, you will learn here.

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The protective shield of our body

The immune system is our external protection. Some war strategists can learn a few tricks from our body's own defense system. The body is in constant exchange with the environment. If the fungi, viruses, parasites or bacteria in it penetrate the human system, a life-threatening infection can arise. Our immune defenses consist of various organs, cells and proteins/proteins. They prevent the penetration of harmful substances, viruses, bacteria, fungi and eliminate toxic substances. They also protect the body from harmful cell changes.

You should know
• Our immune system is our protection and defense
• It consists of several levels of defense
• Our immune system has several strategies
• What is inflammation?
• Why do we get a fever?
• How to strengthen your immune system

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Table of Contents

• Organs of the immune system
• The first barriers
• What are antigens
• Primary lymphatic organs
• Secondary lymphatic organs
• Mucosa-associated tissue MALT
• Several systems in symbiosis result in our immune system
• Defense mechanisms of the immune system
• How does the adaptive immune system work?
• What are antibodies?
• What are the strategies of the immune system?
• What is inflammation?
• Why do we get a fever when we are sick?
• Tips for a strong immune system

The first barriers

Skin and mucous membranes are a mechanical barrier against invaders as well as foreign substances and form our first protective wall to the outside world. They are colonized by beneficial microorganisms, the so-called microbiome. This fends off pathogens. Most pathogens ingested through food or drink are destroyed by stomach acid. Bacteria-inhibiting substances, such as the enzymes in saliva, urine, or tear fluid, prevent the deeper penetration of pathogens. Mucus causes inhaled particles and harmful substances to stick so that they can be transported outward again by the movement of the cilia. Reflexes such as coughing or sneezing also protect the body from external influences. The lymphatic system is also one of the organs of our immune system. It is part of our defense system and is composed of the primary and secondary lymphatic organs and the lymphatic vessels.

What are antigens?

Our immune system is activated primarily by antigens. Antigens are structures foreign to the body. Foreign to the body is not automatically a problem. For example, all foods contain potential antigens. Proteins found on the surface of viruses, bacteria and fungi also act as antigens. If antigens attach themselves to specially designated receptors on our defense cells, specific cell processes are activated. These include the formation of cells that are able to recognize and attack the antigen identified as problematic, but also the formation of so-called memory cells. The information stored in this way during the first contact can be retrieved during a renewed contact. Thus, the human organism can defend itself more quickly in the event of a second contact. Since the immune system basically has the ability to destroy any kind of cell in our organism, its control is of enormous importance. Our cells also have proteins on their surfaces. If these are wrongly classified as dangerous or foreign, while at the same time there is faulty regulation and control, then the immune system attacks the body's own structures. This is then referred to as an autoimmune reaction.

Primary lymphatic organs

The central organ of the immune system is the bone marrow inside our bones. Blood cells are formed here. The T precursor cells mature in the thymus gland above the pericardium.

Secondary lymphatic organs

Actual immune defense takes place in the secondary lymphoid organs (in contrast to the primary lymphoid organs). Mature defense cells move from their place of formation to where they are needed and continue to develop to fight off pathogens and harmful substances. Important secondary lymphoid organs are lymph nodes, which are distributed throughout the body. There are also the spleen and mucosal lymphoid follicles (MALT).

Mucosa-associated tissue MALT
Antigens enter the spleen via the blood. The lymph nodes, which are found almost everywhere, also filter the so-called lymph, in which antigens are also found. About 30% of the 600 lymph nodes are located in the mouth and throat area in order to perceive foreign substances from the outside world as they enter through the existing body orifices. This is also where part of the mucosa-associated tissue (MALT) is located. This is a system of nodular collections of lymphocytes under the mucosa of many organs. In the MALT, contact is made between the foreign substance and the defense cell. As a result, the defense cells take up the fight. Tonsils (NALT = Nasal-Pharyngeal-Associated Lymphoid Tissue) are a part of the MALT and are located in the throat. They enable the defense against pathogens that might otherwise spread along the mucosa of the pharynx. The WALDEYER pharyngeal ring groups together all the tonsils. Here we find tonsils of the tongue, pharyngeal tonsils, palatine tonsils and tonsils at the entrance to the middle ear.

Other parts of the MALT include:

1. Gut-associated lymphoid tissue (GALT),
such as the appendix and the Peyer's plaques in the small intestine
2. Immune tissue in the airways
(BALT = Bronchus-Associated Lymphoid Tissue).
3. Urinary tract lymphatic tissue

Several systems result in symbiosis our immune system

Our body's defenses consist of two complementary and interconnected systems: the innate and the acquired immune system. The innate immune system is non-specific. It consists primarily of phagocytes and killer cells. As a constantly available and immediately deployable primary barrier, it serves primarily to defend against harmful substances and germs that enter our human organism via the skin and the digestive system. The defense response of the acquired immune system, in contrast to the nonspecific defense, is not available until adaptation to the pathogen. The cellular defense uses defense cells (T-lymphocytes) that can attack an opponent directly and uses them on cells that are already infected. The humoral defense, on the other hand, uses antibodies (= defense proteins), which serve to mark the cells for the cellular defense. This is referred to as a learned immune response, since initial contact is a prerequisite for this specialization.

Defense mechanisms of the immune system

Further, in addition to the systems, one can also distinguish the lines of defense. The immune system has three lines of defense. If a pathogen (= disease agent) breaks through one level, the next one takes effect.

First defense The first line of defense of our immune system is the anatomical barrier of our body. Our skin, digestive tract, respiratory tract and mucous membranes. They repel the crudest attacks before they can penetrate further into the human organism. If this first line of defense is weakened, e.g. due to injuries, this increases the risks of disease. However, this is where the second line of defense kicks in. It consists of cells and proteins that attack intruders.

Second defense
The non-specific, humoral defense of the immune system consists of 30 plasma proteins with different properties. These circulate in our blood. Their tasks consist of directly destroying the cell walls of the enemy, marking pathogens, or attracting support.
In the nonspecific cellular defense, everything that the plasma proteins have classified as a danger first meets so-called phagocytes. These take up the pathogens and digest them enzymatically. Examples of phagocytes are macrophages and dendritic cells. They additionally identify the invaders by presenting an antigen on the cell surface. Other immune cells can then recognize this antigen and the acquired response can act.

Third defense
The third line of defense consists of cells that adapt to the pathogen, or antigen, present.

Cells of the innate immune system

Scavenger cells:
Certain cells have the ability to phagocytize pathogens, i.e. they take up foreign substances, microorganisms or tissue parts and dissolve them by means of enzymes. They are also called phagocytic cells. These scavenger cells, called monocytes, are formed in the bone marrow and are already present in the newborn. Through contact with cytokines (messenger substances), macrophages, so-called giant phagocytes, are formed from the monocytes. They are large, motile, mononuclear and belong to the cellular immune system.

Granulocytes (part of the white blood cells)
Neutrophil granulocytes are other phagocytes. They rest in the bloodstream and are attracted by substances secreted by the body when pathogens enter the bloodstream. They then leave the bloodstream and enter the tissues to ingest and eat pathogens. They also clean up destroyed tissue cells. They are present in high numbers in pus.
Eosinophil granulocytes are responsible for killing parasites and viruses and are involved in allergic reactions.
Basophilic granulocytes fight pollutants and parasites. They are mainly involved in allergic processes.
NK cells:
NK cells are natural killer cells and belong to the lymphocytes, a subgroup of leukocytes (white blood cells). Their task is to recognize and kill abnormal cells, such as virus-infected cells or tumor cells. They do not possess antigen-specific receptors.

Dendritic cells
Dendritic cells are highly specialized antigen-presenting cells (foreign molecules are made visible) that also have a feeding function. They recognize invading pathogens, eat them and present a fragment on their cell surface. This enables them to initiate and regulate an antigen-specific immune response. They are the interface between innate and learned immune systems.

What are the cells of the adaptive immune system?

Other killer cells are the cytotoxic T cells. They recognize pathogens and, by binding to specific receptors, can initiate a chain of reactions that can lead to apoptosis (cell death). There are millions of different T cells. Each T cell recognizes a specific pathogen (disease agent).

Different T cells have different tasks:
Memory T cells remember pathogens that have come into contact with the body.
Cytotoxic T cells destroy the body's own cells that are infected with a virus.
T helper cells often help other cells, such as B cells, by releasing cytokines (= messenger substances). These bind to other cells in the body and signal or activate them.
Regulatory T cells are a way of controlling the learned immune system. They stop attacks from other immune cells when the pathogens are removed. This helps to stop, or slow down, the immune response so that it does not get out of control.

B-lymphozyten are the only cells capable of becoming plasma cells, which in turn secrete antibodies. Together with T-cells, they make up the crucial component of the learned immune system. B lymphocytes originate in the bone marrow, from where they travel to the lymphoid tissue where they are activated. In the blood and lymphoid tissue, they encounter foreign substances, adapt to them, and then produce antibodies (also called immunoglobulins), which then initiate destruction.

What are antibodies?

Antibodies are proteins that have different compositions depending on which antigen they bind to. They are produced in B lymphocytes and plasma cells. After production and release, the body's own antibodies combine with the antigen of the pathogen (e.g. in the envelope of bacteria and viruses). This marks the invaders and scavenger cells can detect them (opsonization). In addition, antibodies can neutralize toxins (neutralization). Immunoglobulins bind to the surface structures of the viruses so that they cannot penetrate human cells and multiply. The body is now ready to destroy the pathogens, or infected cells.

What are the strategies of the immune system?

Our body has developed a few effective strategies to eliminate pathogens and remove the body's own non-functioning cells. This happens because not all cells develop as intended, or they become non-functional after some time. This affects approximately 50 million cells per second. These cells must be properly removed, otherwise, among other things, tumors (cancer) could develop.

Physical impacts, such as cuts, burns or pollen, also put a strain on our immune system, as tissue damage can occur here. In order for new healthy cells to have enough space available, old and non-functioning cells must be removed. The penetration of pathogens, e.g. through open wounds, must also be prevented.

Two well-known strategies are the development of inflammation and the increase in body temperature (fever).

What is inflammation?
If our system detects destroyed or non-functional tissue, the blood vessels in the surrounding area dilate to be able to transport more immune cells to the affected area with the blood. If pathogens wait at this sensitive spot, a battle ensues between the defense forces and the invaders. The remains of this battle meet us as pus. Inflammation refers precisely to this fight of the pathogens against our immune system. A short-term inflammation as part of an effect is perfectly normal. On the other hand, a permanent inflammation of a tissue or of the whole body can be worrying. Often autoimmune patients have many inflammations in the body that run largely in the background but are always there. These are then called silent inflammations.

Why do we get a fever when we are sick?
By increasing the body temperature, our system can speed up the metabolism and thus our defenses. In addition, pathogens thrive worse. Our immune system can work more effectively with fever than under normal body temperature. In the long term, fever is problematic for the work of a large number of enzymes in the body. Enzymes function optimally at a normal body temperature. If the body temperature is elevated, for example in the case of severe fever, the structure of the enzymes is denatured, i.e. irreversibly destroyed. Prolonged fever therefore has not only positive effects on the human system. However, especially at the beginning of an infection, fever is not too alarming.

Tips for a strong immune system

Next to the nervous system, the immune system is the most complex system of our body. Through an interplay between certain cells, signal substances and tissues, a defense against pathogens takes place at various levels.
How can we strengthen our immune system?
• Reduce stress
• Sufficient exercise in the fresh air
• Soak up the sun and/or substitute vitamin D sensibly
• Pay attention to a healthy and balanced diet
• Drink enough water