Histamine explosion: how an immediate allergic reaction develops

Гистаминовый взрыв: как развивается аллергическая реакция немедленного типа

It is believed that every fifth person in the world has experienced an allergy episode at least once in their life. All doctors, regardless of specialty, face the problem of allergic reactions in practice. At the same time, there is a steady increase in the number of people with atopic dermatitis, eczema, bronchial asthma and allergic rhinitis.

Occurrence of anaphylactic reactions: anaphylactic shock, status asthmaticus, Quincke's edema, − may pose a direct threat to the life of the patient. Understanding the key mechanisms of hypersensitivity reactions is necessary for physicians of all specialties. Read more about the classification of allergic reactions, as well as the pathogenesis of anaphylaxis, on estet-portal.com in this article.

What provokes the occurrence of allergic reactions of the immediate type

Allergy is an immunopathological reaction of the body, which is accompanied by damage to its own tissues.

At the heart of allergic reactions is the mechanism of sensitization – hypersensitivity of the organism to a certain antigen.

Antigens are subdivided into exogenous – come from the external environment, and endogenous – the human body's own proteins.

Exogenous allergens are of plant, animal, infectious and synthetic origin. They enter the body by inhalation with dust, ingestion with food, parenteral administration or mechanical contact with them. Exogenous allergens most often provoke the occurrence of allergic reactions of the immediate type.

Endogenous allergens – these are the body's own proteins that have changed their structure under the influence of infectious or non-infectious factors: viruses, burns, ultraviolet radiation, etc.
The classification of allergic reactions, as well as the pathophysiological mechanisms of anaphylaxis development, are described further in the article.

Classification of allergic reactions: modern approaches and terminology

There are several approaches to the classification of allergic reactions. Depending on the rate of manifestation of the hyperergic immune response, there are:
• Immediate allergic reactions – appear within the first 20 minutes after contact of the sensitized organism with the allergen: for example, anaphylactic shock;
• Delayed allergic reactions – manifest 24 hours or more after the contact of the sensitized organism with the allergen: for example, the reaction of a person to tuberculin injections.

The most informative is the classification of allergic reactions according to Coombs and Gell, according to which the following types are distinguished:
1.   Anaphylactic reaction;
2.   Cytotoxic reaction;
3.    Immune complex reaction;
4.   Delayed-type hypersensitivity.
The article describes in detail the pathophysiological aspects of the occurrence of anaphylactic reactions, which are also immediate-type allergic reactions.

Type 1 allergic reaction: mechanism of anaphylaxis

A type 1 allergic reaction has several stages of development. The following stages of the formation of the body's hypersusceptibility to the action of the antigen should be distinguished:
1.   Primary entry of the antigen into the body: for example, inhalation of dust or animal hair;
2.   Absorption of antigen macrophages and their presentation to
T-helpers;
3.   Activation of B-lymphocyte clones by T-helpers, which leads to their transformation into plasma cells;
4.   Production of reagins by plasma cells – class E and G4 immunoglobulins;
5.   Sensitization:

Repeated entry of an antigen into the body (for example, dust, animal hair, medication) leads to degranulation of basophils containing reagins on the surface, and the release of mediators of the anaphylactic reaction: histamine, eosinophil migration factor, leukotrienes, and many others. These biologically active substances act on target cells, and, first of all, – smooth muscle.

In addition, these mediators can significantly increase vascular permeability.

This can lead to the following:•   Generalized dilatation of blood vessels (anaphylactic shock);
•   Spasm of the smooth muscles of the bronchi (an attack of bronchial asthma);
•   Massive swelling of the mucous membranes (Quincke's edema);
•   Spasm of the smooth muscles of the intestines (diarrhea).

The effect of histamine on the nerve endings leads to such a manifestation of allergy as itching, and the expansion of small arterioles due to the relaxation of the smooth muscles of the vascular wall leads to the development of an allergic rash.

Thus, the mechanism of development of anaphylaxis becomes clear – a generalized hypersensitivity reaction of a sensitized organism in response to repeated exposure to an antigen. Thank you for staying with estet-portal.com. Read other interesting articles in the "Dermatology" section.