The immune system: structure and function

The immune system is responsible for the persistence of the internal environment of the body. This means that all the alien, penetrated from the outside (bacteria, viruses, parasites), or appeared in the course of life (cells due to genetic damage become atypical) must be cleared. The immune system has the ability to distinguish between "his" from "foreign" and to take measures to destroy the latter.

The structure of the immune system is very complex, it consists of individual organs (thymus, spleen), islands of lymphoid tissue scattered through the body (lymph nodes, pharyngeal lymphoid ring, intestinal nodes, etc..), Blood cells (various types of lymphocytes) and antibodies (special protein molecules) .Odni links of immunity is responsible for the recognition of foreign structures (antigens), while others have the ability to remember their structure, others provide for the production of antibodies neutralizing them.

In normal (physiological) conditions antigen (e.g., smallpox virus), the first time entering the body, causes the immune system - it is recognized, its structure is analyzed and the stored memory cells develop antibodies to it, remaining in the blood plasma. Next arrival of the same antigen leads to immediate attack previously synthesized antibodies and its rapid clearance - thus not voznikaet.Pomimo disease antibody in the immune response and participate cellular structure (T-lymphocytes) are capable of releasing enzymes that destroy antigen.

The immune system: structure and function

An allergic reaction is not fundamentally different from the normal response of the immune system to an antigen. The difference between normal and abnormal is the inadequacy of the forces of reaction and the ratio of the reasons why it vyzyvayuschey.Chelovechesky body is constantly exposed to a variety of substances entering into it with food, water and inhaled air, through the skin. Under normal conditions, most of these substances "ignored" by the immune system, they exist so-called refractoriness

When an allergy occurs abnormal sensitivity to substances or physical factors, which begins to form an immune response. What is the reason of breakage of the protective mechanism? Why one person develops a severe allergic reaction to the fact that the other simply does not notice? The unequivocal answer to the question about the causes of allergies is not received. The sharp rise in the number of sensitized individuals in recent decades can be partly explained by a great number of new compounds that they face in everyday life. This synthetic fabrics, perfumes, dyes, pharmaceuticals, food additives, preservatives and others. The combination of antigenic overload the immune system with inherent structural features of certain tissues, as well as stress and infectious diseases can cause a failure in the regulation of defense reactions and allergy development of host Prednisone.

All this concerns the external allergens (ekzoallergenov). Besides these, there are allergens internal origin (endoallergeny). Some body structures (eg, lens) is not in contact with the immune system - this is required for their normal functioning. But certain pathological processes (trauma or infection) is a violation of a natural physiological isolation. The immune system, finding previously inaccessible structure, perceives it as foreign and begins to react by forming antitel.Esche one embodiment of internal allergens - to change the normal structure of a fabric under the influence of burns, frostbite, exposure or infection. Changes in the structure becomes a "foreign" and triggers an immune response

The immune system: structure and function

All types of allergic reactions are based on a single mechanism, in which several stages can be distinguished.

The classification of allergic reactions

Despite the overall appearance of the mechanism, allergic reactions are distinct differences in the clinical manifestations. The existing classification distinguishes the following types of allergic reactions:

Type I - anaphylactic or allergic reactions of the immediate type. This type of interaction is due to antibody groups E (IgE) and G (IgG) antigen complexes formed and settling on the membranes of mast cells. This released a large amount of histamine, which has a pronounced physiological effect. Time of occurrence of the reaction - from several minutes to several hours following antigen into the body. To this type belong anaphylactic shock, urticaria, atopic asthma, allergic rhinitis, angioedema, allergic reactions in many children (for example, food allergies).

Type II - cytotoxic (or cytolytic) reactions. In this case, G and M immunoglobulins groups attack the antigens that are part of the body's own cell membranes, resulting in cell death and destruction (cytolysis). The reactions are slower than the previous ones, the full development of the clinical picture occurs in a few hours. For reactions of type II include hemolytic anemia and hemolytic jaundice with newborn rhesus conflict (in these conditions there is massive destruction of red blood cells), thrombocytopenia (platelets are killed). This same rank as complications of blood transfusion (blood transfusion), the introduction of drugs (toxic and allergic reaction).

Type III - immunocomplex reaction (Arthus phenomenon). A large number of immune complexes comprised of the antigen and antibody molecules of groups G and M, is deposited on the inner walls of the capillaries and cause damage. Reactions occur within hours or days after the interaction of the immune system with an antigen. To this type belong to the pathological processes of reactions in allergic conjunctivitis, serum sickness (immune response to the serum), glomerulonephritis, systemic lupus erythematosus, rheumatoid arthritis, atopic dermatitis, hemorrhagic vasculitis.

Type IV - late hypersensitization or allergic reactions of delayed type, developing over days or more after the intake of the antigen. This type of reaction occurs with the participation of T-lymphocytes (hence their name another - cell mediated). The attack on the antigen provided no antibodies, and specific clones of T-lymphocytes multiply after previous antigen revenues. Lymphocytes isolated active substances - lymphokines that can cause inflammatory reactions. Examples of diseases that are based on a type IV reaction, - contact dermatitis, asthma, rhinitis.

Type V - stimulating hypersensitivity reactions. This type of reaction is different from all previous ones in that the antibodies interact with cell receptors intended for hormone molecules. Thus, antibodies "substitute" a hormone with its regulatory action. Depending on the particular receptor and receptor antibodies consequence of contact with V-type reactions may be stimulation or inhibition of organ function.