Specific globulins formed by the body under the action of antigen are called antibodies. Their special properties include the ability to connect with the antigen that caused their formation, as well as ensuring the protection of the body from the effects of infectious pathogens. Antibodies are neutralizers of infectious agents that lower the susceptibility of the latter to the effects of complement or phagocytes.
There are two categories of antibodies:
- Precipitating, or complete. Their interaction with the antigen gives a visible immunological process, such as precipitation or agglutination reactions .
- Non-precipitating, or incomplete. This is a category of blocking antibodies. They do not give a visible reaction at the time of connection with the antigen.
The content of antibodies in human serum
Antibodies have different effects on microorganisms: antitoxic, antimicrobial and anticellular. There are antibodies that neutralize viruses and immobilize spirochetes.
Antibodies are differentiated by those that stick together red blood cells (hemagglutinins), dissolve red blood cells (hemolysins) and kill animal cells (cytotoxins).
Autoantibodies act against their own protein in the destruction of organs and tissues. They are produced by the release of antigen with changes in the chemical structure of the body.
Circulating antibodies can be detected in the blood serum. This is an antibody test based on immunological reactions such as complement binding, precipitation or agglutination. It shows both intracellular and cell-related forms.
Immunity. Antibody Functions
The serum of a healthy person contains natural antibodies. These are bodies that provide immunity. Their formation, according to immunologists, occurs according to three main mechanisms:
- Genetic conditioning without antigenic stimulus.
- The reaction of the body to minor attacks of infections that are unable to cause disease.
- The response of the human body to the group effect of microorganisms or food antigen.
The chemical structure of antibodies
Antibodies are closely related to the whey protein fraction of Y-globulin . In its absence, the disease agammaglobulinemia occurs, in which antibodies are not produced by the body. Immunoglobulins are divided into five, different in chemical structure and biological functions, classes: G, A, M, D, E.
Class G immunoglobulins, or igG antibodies, play the most important role in the formation of immunity in the manifestation of various forms and types of diseases.
The accumulation of igG antibodies in the body occurs gradually. At the very beginning of the disease, their number is small. But as the clinical picture develops, the number of antibodies begins to grow rapidly, providing a protective function of the body.
The structure of immunoglobulins
The structure of class G immunoglobulin is a monomer molecule of 4 polypeptide protein bonds. These are two pairs, each of which consists of one heavy and one light chain. At the ends of the chains, each pair has a section, the so-called "active center". The center is responsible for binding to the antigen causing the formation of antibodies. IgG antibodies have two “active centers” at their endings. Therefore, they are divalent and are able to bind two antigen molecules. Antibodies are a neutralizing factor in infectious manifestations.
Under an electron microscope, the igG molecule has the shape of an elongated ellipse with blunt ends. The spatial configuration of the active part of the antibody resembles a small cavity corresponding to an antigenic determinant, just as a keyhole corresponds to a key.