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ALLERGY

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

ALLERGY - an unusual (increased) sensitivity of the body to the effects of certain environmental factors (chemicals, microorganisms and their metabolic products, food products, etc.), called allergens. Allergy leads to the development of allergic diseases.

Allergic diseases are widespread throughout the world and tend to grow. The reasons for the widespread occurrence of these diseases are various. An important role is played by air pollution, the widespread use of antibiotics and other drugs, the emergence of a large number of synthetic materials, dyes, washing powders and other various industrial and household substances, many of which can be allergens.

Various compounds can be allergens - from simple chemicals (bromine, iodine) to the most complex (proteins, polysaccharides). Some of them enter the body from the outside (exogenous allergens), others are formed in the body (endogenous allergens, or autoallergens). Among exogenous allergens, biological, medicinal, domestic, pollen, food, industrial are distinguished.

Biological allergens can be bacteria, viruses, fungi, helminths, serums, and vaccines. The development of many infectious diseases (brucellosis, leprosy , tuberculosis, etc.) is accompanied by an infectious allergy. Diseases caused by bacteria, fungi or viruses, in the development of which allergy plays a large role, are called infectious-allergic. Helminthiasis allergy develops in connection with the absorption of decay products and exchange of helminths.

Almost any drug can be a drug allergen. Due to the significant spread of antibiotics, it is they, and especially penicillin, that most often cause allergic reactions. The frequency of these reactions increases as the course of treatment is repeated. Penicillin more often than other drugs causes fatal allergic reactions, and the dose that causes the reaction can be very small.

Household allergens (house dust, the so-called epidermal allergens - hair, wool, animal dander, daphnia crustacean, which is used as dry food for aquarium fish, household chemicals, especially washing powders) - most often cause allergic diseases of the respiratory tract (bronchial asthma , allergic rhinitis).

Pollen allergens often cause a runny nose, conjunctivitis, and other manifestations of hay fever.

Food allergens (almost all food products; most often milk, eggs, meat, fish, tomatoes, citrus fruits, chocolate, strawberries, strawberries, crayfish), in addition to symptoms (urticaria, fever), cause disturbances in the function of the organs of the gastrointestinal tract ( vomiting, diarrhea).

Industrial allergens (turpentine, mineral oils, nickel, chromium, arsenic, tar, tannins, azonaphthol and other dyes, varnishes, insectofungicides, substances containing bakelite, formalin, urea, epoxies, detergents, aminobenzenes, quinoline derivatives, chlorobenzene, dyes for hair, eyebrows and eyelashes, perfumes, hair fluids; metol, hydroquinone, bromine compounds used in the laboratory of thorium more often cause the development of allergic skin lesions.

A special group of allergens are physical factors - heat, cold, mechanical stress. It is believed that in many cases, under the influence of these factors, certain substances are formed in the body, which become allergens.

In response to the introduction of an allergen into the body, allergic reactions develop that can be specific and non-specific. During specific allergic reactions, three stages are distinguished. In stage I, hypersensitivity to the allergen that first enters the body develops - sensitization. This happens as a result of the production of antibodies that are formed in response to the administration of only a given allergen, or the appearance of lymphocytes that can interact with this allergen. If at the time of their occurrence the allergen is removed from the body, no painful manifestations are noted. With the repeated exposure of the allergen to an organism already sensitized to it, the allergen combines with the formed antibodies or with lymphocytes. From this moment begins the stage of formation of mediators (stage II). As a result, a number of biochemical processes occur with the release of biologically active substances - histamine, serotonin, etc. If the number of mediators and their ratio is not optimal, then they cause damage to cells, tissues, organs. Stage III develops - pathophysiological, or the stage of the clinical manifestation of damage, i.e., the actual allergic reaction. The increased sensitivity of the body in such cases is specific, i.e., it manifests itself in relation to an allergen that previously caused a sensitization state.

According to the development mechanism, specific allergic reactions are divided into 4 types. Each of these types has a specific immune mechanism and its inherent set of mediators. These features determine the clinical picture of the disease.

Type I allergic reactions - immediate type allergic reaction (reagin, anaphylactic or atonic type of reaction). Its development is associated with the formation of antibodies, called "reagins." They relate mainly to the class of immunoglobulins E (IgE). Reagins are fixed on mast cells and basophilic leukocytes. When reagins attach to the corresponding allergen, mediators are released from these cells - histamine , a group of chemotactic factors, heparin , a platelet-activating factor, leukotrienes, etc. Clinical manifestations of the reaction usually occur within 15 to 20 minutes after the sensitized organism contacts a specific allergen (hence the name “immediate reaction” type "). In this case, blisters appear on the skin, bronchospasm, and dysfunction of the gastrointestinal tract are noted. Anaphylactic shock , hay fever, hives, atopic bronchial asthma, Quincke's edema, atopic dermatitis (neurodermatitis), allergic rhinitis (see Anaphylaxis) are allergic reactions of an immediate type.

Some of the mentioned diseases (atopic bronchial asthma , atopic dermatitis, allergic rhinitis , hay fever) belong to the group of so-called atopic diseases (atopos is strange, unusual). In their development, a hereditary predisposition plays an important role - an increased ability to respond with an allergic reaction to the action of exogenous allergens, therefore, in some cases, clarification of the allergological history of the patient's relatives avoids the appointment of potentially dangerous drugs.

Type II allergic reactions - cytotoxic. In this type of reaction, antibodies to tissue cells are formed, which are mainly represented by the IgG and IgM classes. Antibodies bind to the corresponding cells, which leads to the activation of the serum protein complement system. Active complement fragments are formed that cause cell damage and even cell destruction. The cytotoxic type of reaction includes such manifestations of drug allergy as leukopenia , thrombocytopenia, hemolytic anemia, etc. The same type of reaction is observed when homologous antigens enter the body, for example, during blood transfusion (in the form of allergic blood transfusion reactions), and hemolytic disease of the newborn.

III type of allergic reactions - tissue damage by immune complexes (Arthus type, immunocomplex type). The allergen in these cases has a soluble form (bacterial, viral, fungal antigens, drugs, food substances). The resulting antibodies belong mainly to the classes of IgG and IgM. These antibodies are called precipitating for their ability to form precipitate when combined with the corresponding antigen. Under certain conditions, the same precipitate of immune complexes is formed in the body, which leads to the activation of complement, the formation of kinins. Neutrophils phagocytose immune complexes and secrete lysosomal enzymes. Proteolysis is enhanced at the sites of deposition of immune complexes. As a result, tissue damage occurs and inflammation develops as a reaction to this damage. The third type of allergic reaction is leading in the development of serum sickness, exogenous allergic alveolitis, in some cases, drug and food allergies, with a number of autoallergic diseases (rheumatoid arthritis , systemic lupus erythematosus, etc.).

Type IV allergic reactions - delayed-type allergic reaction (delayed-type hypersensitivity, cellular hypersensitivity). In this type of reaction, the role of antibodies is played by sensitized lymphocytes that have structures on their membranes similar to antibodies. The combination of such a lymphocyte with an allergen, which can be on the cells or in a soluble form, leads to the release of a number of substances called lymphokines by the lymphocyte. They cause the accumulation of macrophages, other lymphocytes in this place, as a result of which inflammation occurs.

A delayed type reaction develops in a sensitized organism 1 to 2 days after contact with an allergen. This type of reaction underlies the development of some clinical and pathogenetic variants of the infectious-allergic form of bronchial asthma, rhinitis, contact dermatitis, autoallergic diseases (demyelinating diseases of the nervous system, lesions of the endocrine glands, etc.). It is formed with tuberculosis, leprosy, brucellosis, syphilis and other infectious diseases.

Nonspecific allergic reactions (pseudo-allergic, non-immunological allergic reactions) occur upon first contact with an allergen without prior sensitization. They have only two stages of development - the stage of formation of mediators and pathophysiological. The allergen entering the body itself causes the formation of substances that damage cells, tissues and organs. The composition of mediators and the clinical picture of nonspecific allergic reactions are similar to specific allergic reactions. The following pathways for the formation of mediators in a non-specific allergic reaction are known: the release of mediators of allergy by mast cells under the influence of physical factors (high temperature, ultraviolet radiation, ionizing radiation) or chemical factors (various drugs, for example, radiopaque agents). Massive release of allergy mediators can lead to the development of anaphylactoid shock, their release in the skin - to urticaria, in the bronchi - to bronchospasm.

Activation of complement is possible under the influence of many drugs, bacterial lipopolysaccharides, some endogenously formed enzymes (trypsin, kallikrein, plasmin). This mechanism determines, in particular, hereditary pseudo-allergic Quincke edema.

Violation of the metabolism of arachidonic acid with a shift towards increased formation of leukotrienes is possible under the influence of non-narcotic analgesics (derivatives of salicylic acid, pyrazolone series, non-steroidal anti-inflammatory drugs). The accumulation of leukotrienes in the bronchi leads to the development of bronchial asthma - the so-called aspirin asthma , in the skin - to the development of urticaria and other skin rashes.

Damage caused by the action of immune mechanisms on their own proteins, cells, tissues, is called autoallergy, while damaged proteins, cells, tissues that cause autoallergy are called autoallergens (endoallergens, autoantigens).

Distinguish between natural and acquired autoallergens. Some proteins of normal tissues are natural. Acquired - these are body proteins that have foreign properties during burns, radiation sickness and other processes, as well as when combined with bacterial toxins, drugs, etc. Under normal conditions, there is resistance to own proteins and their own tissues are not damaged, i.e. Sensitized lymphocytes and antibodies (autoantibodies) are not formed against them. With autoallergy, the action of immune mechanisms is directed against their own tissues. This is the essence of the autoallergic process. If tissue damage caused by the action of immune mechanisms becomes quite pronounced, the process becomes an autoallergic disease. Among these diseases are some types of hemolytic anemia, severe muscle weakness (myasthenia gravis), rheumatoid arthritis , glomerulonephritis and a number of other diseases. Autoallergia is involved in the development of rheumatism, ulcerative nonspecific colitis, and in some cases of infectious-allergic bronchial asthma.

In the diagnosis of allergic diseases, a thorough questioning of the patient is very important, in which not only the nature of the disease is established, but also the conditions under which it arose. This suggests that a group of allergens could be the cause of the disease. Specific allergens responsible for the development of the disease are detected using special diagnostic tests and laboratory tests.

Treatment:

  • Discontinuing contact with an identified allergen involves removing the allergen and preventing its action. This can be done with drug and food allergies and much more difficult to do with allergies to house dust, with hay fever during flowering plants, with infectious and allergic diseases.

  • Pathogenetic therapy consists in the use of drugs that block different stages of allergic reactions (immunological, formation of mediators, pathophysiological). Their selection is carried out taking into account the nature of the stage and the type of allergic reaction. So, antihistamines and drugs that block the release of histamine have a positive effect only with type I reactions.

  • Symptomatic therapy is aimed at eliminating certain symptoms of the disease. For example, with a fall in blood pressure, vasoconstrictor drugs are prescribed that normalize it, and with bronchospasm, drugs with a bronchodilator effect.

  • Reducing sensitivity to an allergen is called specific hyposensitization (desensitization). The method is based on the fact that in response to the repeated and gradual administration of the allergen in increasing doses, special, blocking antibodies begin to form in the body, which are believed to bind the allergen and, as it were, prevent its contact with allergic antibodies fixed on tissue cells therefore, allergic cell damage and an allergic reaction do not develop. Specific hyposensitization, as a rule, is carried out during the period when the patient has no signs of the disease.

Prevention of allergic diseases consists in observing measures to prevent repeated contact with substances with a pronounced sensitizing effect, and in preventing violations of the body's protective reactions. To achieve the first goal, limit the intake of medicines, prescribing them only in necessary cases. An important role is played by the introduction of advanced technology at industrial enterprises, which excludes contact with allergens. In apartments, do not allow the accumulation of house dust. The second group of measures includes the elimination of possible foci of chronic infection in the body, which are a source of sensitization. Normalization of the function of the organs of the gastrointestinal tract reduces the possibility of developing food allergies. The most important preventive measure is the feeding of children with breast milk. It was noted that in children who were breast-fed, allergic diseases subsequently develop more often. The correct mode of work and rest is of great importance.