Immune system: this is how our defenses work

Without an immune system, humans could not live. Read how the immune system protects us from pathogens and harmful substances!

Immune system: this is how our defenses work

The immune system protects the body from intruders and pollutants. For this it uses different defense mechanisms. Read more about how the immune system works and its role in transplants and transfusions!

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Immune system: This is how our defenses work

  • What is the immune system?

  • Unspecific defense

  • Specific defense

  • Transplants and transfusions

What is the immune system?

In our environment there are a variety of bacteria, viruses, fungi and parasites, which can sometimes cause life-threatening infections. Pollutants can also make the body sick. The job of the immune system is to prevent such infections and damage.

One differentiates between a nonspecific, innate immune defense and specific defense mechanisms.

Unspecific defense

Non-specific defense includes:

  • External protection functions: They form a first physical and chemical barrier to prevent germs and harmful substances from entering the body. These protective barriers include, for example, the skin itself, the sebum it produces, the mucus on the mucous membranes, the fluid film in the eyes, the flow of urine that cleanses the ureter of germs, saliva, vaginal fluid, and gastric juice.
  • Internal defense mechanismsIf pathogens or foreign substances have been able to penetrate the mechanical and chemical barriers of the skin and mucous membranes, they encounter a second defense front: substances that act against the pathogens (eg interferons, complement system or transferrin), phagocytes, natural killer cells, Inflammatory mechanisms and fever that blocks, for example, the growth of various pathogens and increases the interferon effect.

Specific defense

In addition to the non-specific defense, there is a specific defense system in the body. It specifically targets certain pathogens as well as foreign tissue or blood cells that have entered the body as part of a transplant or a blood transfusion. Substances that the body regards as foreign and cause a defense reaction are called antigens. The specific defense differs from the nonspecific in two important ways:

1. It specifically targets a particular antigen.

2. The body "remembers" the antigen, allowing it to respond faster and more responsively when it reconnects later.

In the specific immune system, different cells and tissues work to fend off foreign substances. These include:

  • B and T lymphocytes (B and T cells, special white blood cells): They perform defense reactions after a certain stimulus (stimulation).
  • Cervical cells (macrophages)
  • antibody

There are two different strategies of specific immune defense:

1. At the Cell-mediated immune response Certain T-cells develop into cytotoxic (= cell-killing) T-cells, which directly attack the invading pathogen or foreign substance.

The cell-mediated immune response is effective primarily against viruses, bacteria and fungi found in body cells against some tumor cells and foreign tissues (grafts).

2. At the by antibody-mediated immune response B cells develop into plasma cells. These produce antibodies (immunoglobulins) and release them. The antibodies each bind specifically to a particular antigen (e.g., bacterial or viral envelope components). For example, they neutralize toxins from bacteria, prevent viruses from adhering to body cells, immobilize bacteria and "eat away" foreign substances and destroyed tissue from food cells.

The antibody-mediated immune response works primarily against pathogens that are outside of body cells and against antigens in body fluids. Depending on where a pathogen is in the body, it can trigger both types of immune response.

Transplants and transfusions

The body uses the immune defense not only against bacteria, viruses and other germs and pollutants, but also against other people's tissues. For example, if someone transplants a donor kidney, their body may reject the foreign kidney. To prevent this, care is taken in the selection of donor organs that the tissue structures of the donor organ as closely as possible resemble the tissue of the recipient.

Even with a blood transfusion, it can lead to a violent defense reaction of the immune system come, if it accidentally blood of a foreign blood group is transmitted: The body has namely antibodies against features of those blood cells that do not circulate in the body.For example, a person with blood group A has antibodies against blood group B, a person with blood group B has antibodies against blood group A.


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