antibody, also as Immunoglobulins play a central role in the human immune system. These macromolecules circulate in the blood and mediate the humoral immune response of all higher vertebrates.
Plasma cells are cells of the immune system and are used for the production and formation of antibodies. Orange: plasma cells, white: antibodies. Click to enlarge.
antibody are proteins found in the blood, on immune cells and in extracellular tissue fluid. Their production is triggered by an antigen (generating antibodies).
Antigens are usually foreign substances, for example surface structures on pathogens such as bacteria or viruses. Antibodies recognize and bind these antigens, whereupon the pathogen is neutralized and eliminated.
They are released into the blood by a class of white blood cells called plasma cells. The plasma cells are differentiated B lymphocytes. B lymphocytes, in turn, are a specific class of white blood cells. Each B lymphocyte recognizes a specific antigen. The contact with "its" antigen activates the B-lymphocyte and starts the production of antibodies directed against this antigen.
If antibody When they come into contact with their antigen, they trigger a humoral immune response to it. Its three main functions are neutralization, opsonization and the activation of the complement system. They do all of this by binding their antigen.
An antibody is a large molecule with a Y-shaped structure. The trunk of the Y and the lower part of the two short arms belong to the so-called constant domain. It is identical for all antibodies of the same class or the same isotype. The variable domains are located at the ends of the two short arms of the Y-wing.
They form the specific antigen binding sites that recognize a very specific "epitope" on the surface of an antigen. An epitope is a submolecular structure, for example a short section of a surface protein of a bacterium (the surface protein would then be the antigen).
Thanks to the two arms, each antibody can bind two of "its" epitopes and thus cross-link several antigens with one another, which is known as agglutination.
Neutralization: Antibodies neutralize toxins, bacteria and viruses by attaching to them and preventing them from entering human cells.
Opsonization: When an antibody has bound its antigen, it marks it for other immune cells such as scavenger cells (phagocytes), which then eliminate the antigen.
Complement system: This is a cascade of over thirty proteins that successively bind to the surface of microorganisms (e.g. a bacterium) and trigger several immune mechanisms. They can mark the bacterium for phagocytes, trigger inflammatory reactions or lead directly to lysis by driving pores into the cell membrane. An antibody bound on the surface of a bacterium can activate the complement system via the so-called "classic way".
An increased titer of Antibodies in the blood indicate an ongoing immune response and therefore an infection. You can also tell from the presence of antibodies whether someone has been vaccinated against certain diseases. The antibodies themselves mediate vaccination protection. In passive immunization, the patient is injected directly with antibodies directed against a specific pathogen. This vaccination protection does not last long, as the injected antibodies are broken down over time and cannot be reproduced.
In active immunization, antigens rather than antibodies are injected. These can be weakened or killed pathogens or parts of pathogens (purified surface molecules from viruses and bacteria). The immune system of the vaccinated person then recognizes epitopes on the injected antigens and produces antibodies against them. If the vaccinated person later comes into contact with the pathogen, the antibodies that are already present immediately trigger an immune response.
The pathogens are eliminated before they can cause disease. Some vaccines (for example against the childhood diseases measles, mumps and rubella) can provide lifelong immunity. So active immunization is usually preferable to passive, provided that the vaccine is safe.
Disturbed antibody production (e.g. due to inherited B-cell defects) triggers various immune deficiency diseases. When antibodies bind to the body's own epitopes and then trigger an immune response, autoimmune diseases occur.