ALLERGY

ALLERGY is an unusual (increased) sensitivity of the organism to the influence of certain environmental factors (chemicals, microorganisms and their products, food products, etc.), called allergens. Allergies lead to the development of allergic diseases.

Allergic diseases are widespread all over the world and tend to grow. The reasons for the wide spread of these diseases are different. An important role is played by air pollution, widespread use of antibiotics and other medicines, the emergence of a large number of synthetic materials, dyes, washing powders and other diverse industrial and household substances, many of which may be allergens.

Allergens can be various compounds - 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 itself (endogenous allergens, or autoallergens). Among the exogenous allergens are biological, medicinal, household, pollen, food, industrial.

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 an important role is played by an allergy, is called infectious-allergic. Allergy in helminthiases develops due to the absorption of the products of decay and the exchange of helminths.

A medicinal allergen can be practically any drug. In connection with the significant spread of antibiotics, they, and especially penicillin, most often cause allergic reactions. The frequency of these reactions increases with the course of treatment. Penicillin is more likely than other drugs to cause allergic reactions with a fatal outcome, and the dose causing the reaction can be very small.

Household allergens (home dust, so-called epidermal allergens - hair, wool, animal dander, daphnia crab, 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 , An allergic rhinitis).

Pollen allergens more often cause a runny nose, conjunctivitis and other manifestations of pollinosis.

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 gastrointestinal tract disorders Vomiting, diarrhea).

Industrial allergens (turpentine, mineral oils, nickel, chromium, arsenic, tar, tannins, azonaphthol and other dyes, varnishes, insectophangicides, substances containing bakelite, formalin, urea, epoxy resins, detergents, aminobenzenes, quinoline derivatives, chlorobenzene, dyes For hair, eyebrows and eyelashes, perfume substances, hair liquids used in photolaboratories of metol, hydroquinone, bromine compounds) often cause the development of allergic skin lesions.

A special group of allergens are physical factors - heat, cold, mechanical effect. 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, which can be specific and nonspecific. In the course of specific allergic reactions, three stages are distinguished. In the first stage, there is an increased sensitivity to the first-ever allergen in the body - sensitization. This occurs as a result of the development of antibodies formed in response to the introduction of only this 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 already sensitized organism, the allergen combines with the formed antibodies or with lymphocytes. From this moment the stage of formation of mediators begins (II stage). 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, they cause damage to cells, tissues, organs. The third stage develops - pathophysiological, or the stage of clinical manifestation of damage, ie, the actual allergic reactions. The increased sensitivity of the organism in such cases is specific, ie, it manifests itself in relation to the allergen, which previously caused a state of sensitization.

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

I type of allergic reactions - allergic reaction of immediate type (reactive, anaphylactic or atonic type of reactions). Its development is associated with the formation of antibodies, called "reactive". They relate mainly to the class of immunoglobulins E (IgE). Reagins are fixed on mast cells and basophilic leukocytes. The mediators, histamine, a chemotactic factor group, heparin , a platelet-activating factor, leukotrienes, etc., attach the reactants with the corresponding allergen from these cells. Clinical manifestations of the reaction usually occur 15 to 20 minutes after the sensitized organism contacts a specific allergen (hence the name "immediate reaction Type "). At the same time, blisters appear on the skin, there is bronchospasm, a disturbance of the function of the gastrointestinal tract. Allergic reactions of immediate type include anaphylactic shock , hay fever, urticaria, atopic bronchial asthma, Quincke's edema, atopic dermatitis (neurodermatitis), allergic rhinitis (see Anaphylaxis).

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

II type of allergic reactions - cytotoxic. In this type of reaction, antibodies to tissue cells are formed, mainly represented by the classes IgG and IgM. The antibodies bind to the corresponding cells, which leads to the activation of the serum protein complement system. Active fragments of complement are formed, which cause cell damage and even their destruction. Cytotoxic type of reactions include 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, with blood transfusions (in the form of allergic blood transfusion reactions), with hemolytic disease of newborns.

III type of allergic reactions - tissue damage by immune complexes (Arthus type, immunocomplex type). Allergen in these cases has a soluble form (bacterial, viral, fungal antigens, drugs, food substances). The resulting antibodies refer primarily to the classes IgG and IgM. These antibodies are called precipitants for their ability to form precipitates when combined with the appropriate 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 phagocytize immune complexes and at the same time secrete lysosomal enzymes. Increases proteolysis in places of deposition of immune complexes. As a result, tissue damage occurs and the inflammation develops as a reaction to this damage. The third type of allergic reactions is leading in the development of serum sickness, exogenous allergic alveolitis, in some cases, drug and food allergies, with a number of auto-allergic diseases (rheumatoid arthritis, systemic lupus erythematosus, etc.).

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

The delayed-type reaction develops in the sensitized organism 1 to 2 days after exposure to the 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, auto-allergic 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 (pseudoallergic, non-immunological allergic reactions) occur upon first contact with an allergen without previous sensitization. They have only two stages of development - the stage of mediator formation and pathophysiological stage. The allergen that enters the body causes the formation of substances that damage cells, tissues and organs. According to the composition of mediators and the clinical picture, nonspecific allergic reactions are similar to specific allergic reactions. Known are the following ways of mediator formation in a nonspecific allergic reaction: the release of mediators of allergy by mast cells under the influence of physical (the action of high temperature, ultraviolet irradiation, ionizing radiation) or chemical factors (various drugs, eg radiocontrast agents). Massive release of mediators of allergy 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 endogenous enzymes (trypsin, kallikrein, plasmin). This mechanism determines, in particular, the hereditary pseudoallergic edema of Quincke.

The disruption of the metabolism of arachidonic acid with a shift toward enhanced leukotriene formation is possible under the influence of non-narcotic analgesics (derivatives of salicylic acid, pyrazolone series, nonsteroidal 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 autoallergeny, the damaged proteins, cells, tissues that cause autoallergeny are referred to as autoallergens (endoallergens, autoantigens).

There are natural and acquired auto-allergens. Some proteins of normal tissues are natural. Acquired are the proteins of the body, which appear to have foreign properties for burns, radiation sickness and other processes, as well as for combining with bacterial toxins, drugs, etc. Under normal conditions, there is resistance to own proteins and own tissues are not damaged, i.e., No sensitized lymphocytes and antibodies (autoantibodies) are formed against them. With auto-allergy, the action of immune mechanisms is directed against their own tissues. This is the essence of the auto-allergic process. If tissue damage caused by the action of immune mechanisms becomes sufficiently pronounced, the process becomes an auto-allergic disease. Among these diseases are some types of hemolytic anemia, severe muscle weakness (myasthenia gravis), rheumatoid arthritis, glomerulonephritis and a number of other diseases. Assume the participation of auto-allergy in the development of rheumatism, ulcerative nonspecific colitis, in some cases, infectious-allergic bronchial asthma.

In the diagnosis of allergic diseases, a thorough questioning of the patient is important, in which not only the nature of the disease is established, but also the conditions under which it arose. This makes it possible to guess which 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:

• Termination of contact with the revealed allergen includes removal of the allergen and prevention of its action. This can be done with drug and food allergies and is much more difficult to do with allergies to house dust, with pollen during flowering plants, with infectious and allergic diseases.

• Pathogenetic therapy consists in the use of drugs that block different stages of allergic reactions (immunological, mediator formation, 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 in type I reactions.

• Symptomatic therapy is aimed at eliminating individual symptoms of the disease. For example, with the fall of blood pressure, vasoconstrictive drugs are prescribed that normalize it, and for bronchospasm - drugs that have a bronchodilator effect.

• The decrease in sensitivity to an allergen is called specific hyposensitization (desensitization). The method is based on the fact that, in response to repeated and gradual introduction of an allergen into the body in increasing doses, special blocking antibodies are beginning 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 , And consequently, allergic cell damage and allergic reaction do not develop. Specific hyposensitization is usually carried out at a time when the patient has no signs of disease.

Prevention of allergic diseases is the observance of measures that prevent repeated contacts with substances that have a pronounced sensitizing effect, and in preventing violations of the body's defenses. To achieve the first goal, they restrict the intake of medicines, appointing them only in necessary cases. An important role is played by the introduction at industrial enterprises of advanced technology, which eliminates the contact of workers with allergens. In flats, house dust should not be allowed to accumulate. The second group of measures includes the elimination of possible foci of chronic infection in the body, which are the source of sensitization. Normalization of the function of the gastrointestinal tract reduces the possibility of developing food allergies. The most important preventive tool is the feeding of children with breast milk. It was noted that in children who were on artificial feeding, allergic diseases subsequently develop more often. The correct regime of work and rest is of great importance.