Antibodies are an important part of our immune system. You have certainly heard of them in the context of the corona pandemic. You need these proteins to protect yourself from pathogens.
Antibody Definition
antibody or immunoglobulins are proteins used by the immune system. They serve to fight pathogens such as bacteria or viruses. Antibodies recognize exogenous structures that are surface structures on the pathogens.
The specific surface structures are also called antigens. If you would like to learn more about antigens, please have a look at the relevant explanation.
formation of antibodies
Through a reaction of B lymphocytes the antibodies are produced. To put it simply, this is how it works:
When a B cell comes in contact with a matching antigen, they will B cells activated and differentiate themselves plasma cells. These release a larger amount of immunoglobulins. the antigens are specifically bound by antibodies.
However, once you recover from an infection, the specialized B cell is not simply eliminated. She transforms into one B-memory cell. If you come into contact with the same or an almost identical pathogen again, suitable antibodies can be produced immediately without having to have high levels of them permanently.
Antibodies are not always directed against structures that are foreign to the body. In many autoimmune diseases, such as multiple sclerosis, immunoglobulins are formed by the immune system malfunctioning against endogenous structures.
If you want to learn more about autoimmune diseases, then read the explanation on the subject.
Antibody build-up
Several types of antibodies circulate in your body, but their basic structure is similar. They are composed of light and heavy protein chains. The two chain types each consist of two different domains. One of them is variable, the other is not. They represent a kind of scaffold. The different components of an antibody are connected to one another by disulfide bridges (-SS-).
disulfide bridges are compounds of two sulfur atoms. They can only be formed between two cysteine amino acids. In addition, they serve to cross-link proteins.
Figure 1: Schematic structure of an IgG antibody, 1 – Fab section, 2 – Fc section, 3 – heavy chains, 4 – light chains, 5 – antigen binding site, 6 – hinge-Region (hinge) Source: wikipedia.de
antibody binding
Immunoglobulins bind antigens specifically. Binding works after Key-lock principle. The regions of the antigens to which binding occurs are called epitopes.
The site of the antibody that is complementary to the epitope – which is like the lock to the key – is called a paratope. The paratope is formed by the variable regions of the heavy and light chain of the antibody.
function of antibodies
When foreign organisms enter the body, their antigens are recognized by the immune system. It will B cells (B lymphocytes) activated and they produce specific antibodies. The antibodies are specifically directed against the invader’s antigen – they bind there according to the key-lock principle.
The surface of a bacterium or virus is marked as non-self when recognized by an immunoglobulin. In addition, the spread of the invader is contained by the antibody binding. In addition, the immunoglobulins block important surface proteins of the pathogen. You can find out more about this in the following sections.
importance in the immune response
Antibodies meet within a immune response multiple functions. On the one hand, they ensure that invading pathogens are blocked and combated. As a result, they cannot unfold their harmful effects. Interaction with the body’s own cells is also prevented.
Antibodies as markers
It is possible for antibodies to mark pathogens. This process is called opsonization. Their surface is covered by antibodies and opsonin. This makes it easier for the phagocytic cells to locate and absorb the foreign cells.
Phagocytic cells or scavenger cells are, for example, macrophages or granulocytes, which can absorb bacteria, among other things.
The uptake of macromolecules is also called phagocytosis.
binding with killer cells
There is a possibility that antibodies natural killer cells tie. Then the immunoglobulins can control the killer cell and direct it to destroy other cells or pathogens. If a pathogen has attacked a cell, the antibody is able to direct the killer cell in such a way that it only fights and destroys the pathogen or the infected part of the cell, but not the entire cell.
agglutination
Usually several antibodies bind to several pathogens at the same time, as you can see in Figure 3. This process is also called agglutination. The resulting antigen-antibody complexes are insoluble and are deposited in the tissues or blood vessels (precipitation). The clumps can then be attacked by special cells in the immune system, such as the macrophages (phagocytes)be absorbed and digested.
classes of antibodies
There are several types of antibodies (classes). The classification is based on slight structural differences as well as special functions or sites of use of the antibodies. Here you can see an overview:
class
shape
location
function
IgA
two linked antibodies (dimer)
mucous membranes
Pathogen detection and defense in the airways and digestive tract
IgD
monomeric
All body fluids
activation of
lymphocytes
IgE
monomeric
Bound to mast cells
First defense at the
Body surface, often directed against parasites
IgG
monomeric
Mainly lymph
main class to
antigen binding
IgM
five linked antibodies (pentamer)
blood
unspecific primary defense in the blood
Monoclonal Antibodies
as Monoclonal Antibodies are active proteins that are produced by a single cell line. This cell line goes back to a B lymphocyte and is specific to a epitope designed.
As a rule, however, antibodies are directed against several epitopes of a pathogen. In this context one also speaks of polyclonal antibodies.
Monoclonal antibodies are of great importance in diagnostics and research because they have a high specificity with which they can bind a large number of macromolecules. You can practically target and fight a pathogen.
Reports by the RKI showed, for example, that the allocation of monoclonal substrates can reduce the severity of a Covid-19 course.
antibody test
Antibody tests are used to find out whether the immune system has fought against a specific pathogen before.
For example, if you want to find out whether you have ever been infected with Corona, you can do an antibody test.
For the antibody test, blood is placed on a test surface with fragments of the pathogen. If the blood has antibodies, they will react with fragments of the virus or bacteria, for example, on the test. A bond is formed. This can then be verified by a color reaction.
Today, antibodies are used in research and diagnostics to fight diseases such as cancer. They are intended to release a kind of brake in the immune system so that the body’s own defenses can come into play and destroy the tumor. On the other hand, antibodies are to be used as «lure cells» that lead the killer cells to the tumor. In addition, they can Block growth signals from tumor cells. But how does antibody therapy work?
Antibody therapy process
As you already know, specific antibodies bind to epitopes of an antigen. This is how they render antigens harmless. In the case of cancer, for example, the body’s own cells are diseased, which are not actually fought by the immune system because they are not recognized as being foreign to the body. However, tumor antigens and corresponding epitopes to which immunoglobulins can bind are located on the cells. And that is exactly what is done in antibody therapy. Monoclonal antibodies are used in a targeted manner to bind to the epitopes and cause the tumor cell to die
Antibody therapy using the example of breast cancer
One type of antibody therapy can be well explained using the example of breast cancer. Because not all antibody therapies are the same, they are tailored to the disease.
Certain antibodies, in this case the HER2 antibodies, block the HER2 receptors of the tumor cell. She dies as a result.
The HER2 receptor is a protein on the cell surface. This protein sends growth signals, causing cells to multiply as they are supposed to as a natural process of cell division. However, if too many signals are sent out, uncontrolled cell division and excessive, pathological growth occur.
However, antibody therapies as well as chemo therapies do not run without the occurrence of side effects. Dizziness or nausea can also occur here. There is also a risk that allergies may occur. Other side effects are also possible.
Antibodies – The Most Important
- Antibodies, also called immunoglobulins, are formed when they come into contact with antigens.
- Antibodies can also turn against your own body, a condition called an autoimmune disease.
- They are made up of two light and two heavy protein chains.
- Antibodies bind to a specific section of the antigen, the so-called epitope, according to the key-lock principle.
- The antibodies formed in the body are polyclonal, they respond to several epitopes, monoclonal antibodies are also produced (artificially), they only react specifically to one epitope.
- Antibody tests are carried out to determine the amount of certain antibodies in the organism.
proof
- dzif.de: antibodies (08/06/2022)
- chemeurope.de: antibodies (07.08.2022)
- antibodies-online.de: antibodies (07.08.2022)
- gesundheitsforschung-bmbf.de: antibodies (07.08.2022)
- daskwort.de: Antibody therapy (08.08.2022)