Protein molecules have a complex structure and consist of amino acids. The latter are the material for the assembly of proteins, which is why any living organism needs their constant replenishment. The main source of amino acids is any dietary protein that must enter the body's digestive system and be broken down into elemental components. At the same time, food proteins that have entered the human blood are immunogenic substances, whose presence inside the vessels is unacceptable. Any foreign protein that comes into direct contact with the internal environment of the body harms the latter and acts as an antigen.
Characterization of dietary proteins
In the case of normal eating behavior, which excludes cannibalism, the human digestive system receives mainly those substances that are normal inbodies are absent. This means that all food proteins that enter the human blood are foreign. Therefore, before their assimilation, they must be split into elementary components - amino acids. This need is explained by the fact that any protein has some properties, the presence of which is explained by a specific chemical and spatial structure. Some of them are enzymes and some are poisons.
Any protein retains its properties as long as it has the same spatial structure. And the most reliable and energetically correct way of its assimilation is just complete cleavage, which consists of the stage of denaturation and the gradual breaking of peptide bonds. Without cleavage, all food proteins that enter the human blood are antigens. Moreover, intravenous administration of dietary proteins threatens with rapid death of a person, while the introduction of amino acids or dipeptides into the blood can be used by athletes or malnourished patients with protein starvation without harm to the body.
Contact of foreign proteins with the immune system
When studying immunology and microbiology, as a test designed to determine the level of knowledge of the material, provocative questions may be asked of trainees. For example, a question of a similar nature: food proteins that have entered the human blood are what? If this is computer testing, then the following answers can be offered: antibody, enzyme, antigen, hormone. The only rightan antigen is a variant, since any foreign protein in the internal environment of the body is attacked by the immune system and perceived as a xenobiotic or poison. It also cannot be a vitamin.
Causes of an immune response
An organism is able to use for its needs only those proteins whose primary structure is encoded in its genome. This means that even the entry into the blood of an enzyme that normally exists in humans will cause an immune system response. This will happen due to the inadmissibility of finding certain substances in certain biological media. For example, intracellular enzymes, which are normally present in mitochondria or in the nucleus, are foreign when released into the blood. Therefore, they are perceived by the immune system as antigens and are eliminated by the macrophage system.
The only exceptions are those proteins that fully correspond in structure to some enzymes or hormones. For example, artificially synthesized insulin, when injected into the bloodstream, does not cause an immune response. This is because it has the same chain structure and electrical charge as natural human insulin. However, insulin is not a dietary protein. Once in the human blood, it is a hormone. But all other dietary proteins, when administered intravenously, are significantly harmful.
For successful digestion, food proteins must be broken down in the digestivesystem. Then they can get into the blood already in the form of amino acids, having lost their structure. In this form, they can be used by cells to biosynthesize their non-immunogenic proteins, which will act as hormones, mediators, or enzymes inside the cell or in the blood. The statement that food proteins that have entered the human blood are enzymes, antibodies or hormones is false. They remain only antigens, and cannot be anything else.
Why foreign proteins are not antibodies
To finally understand why a foreign protein cannot be an antibody, you need to correctly understand the course of immune processes. An antibody is a complex globulin protein that is synthesized by plasma cells of the human immune system. And an antigen is a molecule that causes an immune system response. All food proteins that enter the human blood are antigens. Upon initial contact, they are engulfed by a macrophage, which recognizes the structure of the protein and transforms into an antigen-presenting cell. Based on the information obtained after the lysis of the antigen, immunoglobulins are synthesized. The latter are antibodies.
Antibody synthesis
An antibody is a protein molecule synthesized in the human body to eliminate a specific antigen. It is synthesized in response to the appearance of antibodies in the internal environment of the body. The mechanism of their interaction can be expressed as follows: the antibody, in case of contact with the antigen, allows the macrophage to start massdestruction of a foreign protein, bypassing the stage of antigen presentation on its membrane. Antibody synthesis is a way to move from cellular to humoral immunity, and all food proteins that enter the human blood are antigens that must be eliminated.
The outcome of the introduction of dietary protein into the blood
The hypothetical outcome of an intravenous injection of a foreign protein is difficult to predict, as it depends on the specific protein and its dose. In minimal doses, an immune response will develop, and the protein will be taken up by macrophages, which will provide antigens to plasma cells. The latter, after about 2 weeks, synthesize antibodies. In the case of repeated introduction of the protein into the blood, a reaction of not cellular, but humoral immunity will occur. At the same time, food proteins that have entered human blood are not antibodies.
Introduction of proteins in large quantities
In large quantities, dietary proteins introduced directly into the blood will lead to death due to progressive renal failure or pulmonary embolism. The latter option is possible with the introduction of protein in the composition of oil solutions or in the form of solid particles. However, specific experiments designed to confirm such hypotheses were not conducted for ethical reasons.
Obviously, the body cannot absorb proteins from the blood, but uses only the components of which they consisted for its needs. Then the question should be answered: in the case of direct intravenous administration, dietary proteins,that got into the human blood, are antibodies, antigens, enzymes or vitamins? The answer is antigens. Some of them without splitting is poison at all. Getting directly into the blood, they are not neutralized by the liver, and therefore they can kill a person.
