Immunological tolerance

It is known that antigenic activity of various substances is greater, the more they are in the genetic relation to the species of animal, which they sencibilisiruet. Immunological reaction is waning as the antigenic structure of substances, which sencibilisiruet recipient, is close in structure to the tissues of the latter. There is a biological law that the body's own tissue are not for him antigens. This does not apply to isoantigen and antigens of transplanted tissues.
Why the body's own tissue is not sencibilisiruet his or organisms related species? This question remained unsolved for a long time. The discovery of the phenomenon of immunological tolerance Medawar and his school shed new light is antigenic specificity.
There is a hypothesis that explains immunological tolerance as follows: the cells of the body, is able to "recognize" foreign substances and to answer their invasion of cellular immune response (elaboration of appropriate antibodies are formed relatively late in the ontogenesis of the body. In most species of animals such immunocompetent cells appear only in late prenatal period or immediately after birth. Therefore, all potentially allergenic substances, which are formed in the organism to the maturation of these cells remain unchanged and after their maturation.
Thus, the only group of cells is a so-called code in the body. These cells provide individual immunological specificity, which some authors call the self (self organism).
Recent studies have shown that the birthplace of immune cells in the body is the thymus gland (thymus) *. The removal of the thymus in mammals in the prenatal period or immediately after birth causes such a state of the body in which he does not react to the introduction of alien substances, i.e. in the body in response to the introduction antigens are not produced specific antibodies (no immune protection, response). The removal of the thymus in later period after birth, i.e. in the period when immunocompetent cells are Mature, does not cause such an effect.
These immunocompetent cells ensure the preservation of animal species (self).
Immunocompetent cells cease to play its role of protecting the body only after total radiation of x-rays or administration of immunosuppressive drugs (6-mercaptopurine, actinomycin, and others).
You can create a state of relative immunological tolerance, constantly introducing adult animal massive dose of soluble antigen. This so-called state of immunological palsy, which is a transient: gradually the animal is restored to a previous state after a few weeks after cessation injection antigen. The body's ability to protect "their" from "alien" is the most mysterious and interesting in all species of animals. This property is not only the conservation of species specificity of the body of the animal, but also protect it from various disease-causing agents. "Work" of immune cells in the body must be absolutely clear: the slightest violation leads to autodestructive tissues of the animal.
An explanation of all of these phenomena is currently still quite speculative. The most popular clonal theory Barneta - finder. Immunocompetent cells of mesenchyme that appear in utero in lymphoid organs and humoral environments, acquire the ability to "recognize" antigens and to produce antibodies against them. Soon among this group of cells is the group of "main", major. Those in its location more often in contact with all the diverse mosaic of antigens in the body, join with them in immunological conflict and die on the condition of excess antigens in the period of fetal maturation. According to this theory, the "recognition" of "own" and "alien" in the body is not that other, as the steady destruction in the period of embryonic development of all cellular clones that are somehow capable of damaging the "main" body cells. All other cell clones are saved.
Theory of Barneta - finder, like other theories, anyway explaining the biological phenomenon of immunological tolerance, has contradictions. Currently, however, this theory is better than the other, explains such phenomena as immunological tolerance arising in utero transplantation of mesenchymal cells, as well as the state of immunological paralysis when re passive soluble antigen, change of reactivity when exposed his x-rays and application radiometricheskie substances.

* Birds place of education immunocompetent cells is a bag fabritsiusa, about the cecum.- Approx. of the author.