A change in the susceptibility or reactivity of an organism to a foreign substance is called an allergy (from the Greek. "Reaction to someone else"). The name "allergy" was coined by the Austrian scientist Clemens Pirke in 1906. He suggested using the term to describe the action on the body of various factors from the external environment, and call the substances that excite these allergic reactions allergens.
The American allergist R. A. Cook in 1947 created the first classification of allergies. By his definition, there is immediate hypersensitivity and delayed-type hypersensitivity. The latter type will be discussed in detail in this article. What is important, immediate and delayed hypersensitivity reactions are significantly different from each other.
Main difference
Immediate hypersensitivity is a reaction to an antigen that occurs 20-25 minutes after a second meeting with an allergen (antigen). A delayed-type hypersensitivity reaction expressed no earlier than 7-8 hours or a few days. In 1968, P. G. Jell and R. A. Coombs wrote a scientific paper called the New Classification of Allergic Reactions. According to this classification, 4 main types of allergies are distinguished.
Types of Allergies
- Type 1 - anaphylactic, atopic, reagin. The manifestations of this type include Quincke's edema, anaphylactic shock, atopic bronchial asthma, urticaria.
- Type 2 - cytotoxic or cytolytic, its manifestations include leukemia, hemolytic anemia, Rh incompatibility.
- 3 type - immunocomplex, or Arthus type. It is evaluated by the general reaction and is the main one in the etiology of serum sickness, rheumatoid arthritis, systemic erythematosus lupus. All three of these types are closely related to hemagglutinin and belong to immediate hypersensitivity .
- Type 4 - delayed-type hypersensitivity, the counteraction mechanism is characterized by the cellular action of a T-lymphocyte-heller antigen.
Sensitization
Delayed hypersensitivity reaction is the sensitization of the body to microbial antigens, bacteria, viruses, fungi, helminths, to artificial and natural antigens (chemicals, drugs), to individual proteins. The most pronounced delayed-type hypersensitivity reacts to the introduction of low-immunogenic antigens. A small dose of antigens during subcutaneous injection cause delayed hypersensitivity. Development mechanism An allergic reaction of this type is the hypersensitivity of helper T-lymphocytes to antigens. Hypersensitivity of lymphocytes causes the release of substances, for example, interleukin-2, which activate macrophages, the death of the antigen that caused sensitization of lymphocytes occurs. T lymphocytes also include a defense mechanism in which bacteria, viruses, or protozoa die.
This form of sensitization is seen in many infectious diseases, such as tuberculosis, syphilis, brucellosis, diphtheria, mycosis, helminthiasis, and others, as well as transplant rejection.
Example
The most obvious example of such reactions is the Mantoux tuberculin test . If tuberculin is injected intracutaneously to a person in whose body the tubercle bacillus is present, then after 24-48 hours, an induction of 10-15 mm with an abscess in the center is formed at the injection site.
Histological examination shows that the infiltrate consists mainly of lymphocytes and cells of the monocytic-macrophage series.
Aneria
In rare cases, there is a lack of reaction. This is called anergy, that is, the lack of reaction of the body to stimuli.
Positive anergy occurs when an allergen, entering the body, dies. In this case, inflammation does not occur.
Negative anergy occurs when the body cannot defend itself, which indicates the weakness of the individual. The reason for the lack of reaction or its weak expression can be a decrease in the number of T-lymphocytes or a violation of their functions, it can also be caused by increased activity of T-suppressors.
Paraallergy and pseudoallergy
There are the concepts of "paraallergy" and "pseudoallergy." They occur in the diagnosis of infectious diseases, expressed as allergic reactions.
Paraallergy is when an infected body reacts to similar allergens, for example, an infected tuberculosis reacts to atypical mycobacteria.
Pseudoallergy is an allergy, for example, to tuberculin in a person with leukemia.
Allergy Stages
In the allergic period, 3 stages are described:
- Immunological stage. At this stage, all modifications of the immune system occur . The allergen that enters the body combines with antibodies and hypersensitive lymphocytes.
- Pathochemical stage. At this stage, the formation of mediators (biologically active chemicals), monokines, lymphokines, which are formed as a result of the addition of an allergen to antibodies and hypersensitive lymphocytes, takes place in the cells .
- Pathophysiological stage. At this stage, the clinic of the disease appears. This happens because the appeared mediators adversely affect the tissues of the body. At this stage, swelling, itching, spasms of smooth muscle tissue, circulatory disorders, etc. are observed.
These stages determine the delayed-type hypersensitivity.
Treatment
This is one of the most difficult questions. Therapy should be carried out differently from the treatment of immediate hypersensitivity, since delayed-type hypersensitivity is an immune inflammation.
Directivity
Treatment should be aimed at the immunological moment, anti-inflammatory therapy and neutralization of the pathogen. Nevertheless, therapy must be started with the general rules for the treatment of allergic diseases. Be sure to follow a hypoallergenic diet. In the treatment of this type of hypersensitivity, etiological treatment, that is, aimed at the cause of the disease, occupies a special place.
Types of delayed-type hypersensitivity . Their treatment
This type of hypersensitivity is divided into contact, tuberculin and granulomatous, therefore, treatment should be aimed at a certain type.
- Contact hypersensitivity occurs when interacting with chemicals (cobalt, nickel, wood resins, mercury, etc.), drugs, poisonous plants. In addition to the main treatment for allergies, in addition to the treatment of contact hypersensitivity, the termination of interaction with the causes of allergies, therapy aimed at relieving inflammation, and UV radiation are prescribed.
- Tuberculin hypersensitivity is related to diagnosis and is caused by tuberculin or similar antigens, so treatment is not required.
- Slow-type infectious hypersensitivity arises from sensitization to microorganisms that cause infectious diseases, such as tuberculosis, syphilis, brucellosis, anthrax, gonorrhea, parasitic infestations. Treatment of infectious allergies is focused on the destruction of pathogens.
- Allergic hypersensitivity to soluble proteins occurs when the immune system is weakened, in which the body does not take protein compounds, such as milk, fish, eggs, nuts, legumes and some proteins found in cereals. For effective treatment, all foods that cause allergies are excluded from the diet.
- Auto-allergic hypersensitivity is when sensitive lymphocytes and own antibodies are produced on the body’s own tissues, which cause allergies. There are two types of autoallergic allergies.
The first is when the immune function is not damaged, but an auto-allergen occurs that causes a violation of the immune system. The second is when immunity fails, not understanding where its proteins are and where others are, so he believes that this is an allergen. The treatment is symptomatic and pathogenetic, which is the use of immunosuppressants. These are mainly corticosteroids.
Hypersensitivity during transplantation is the destruction of a foreign body introduced into the body. This allergy can be prevented by the correct selection of a donor, as well as prescribing various immunosuppressants to inhibit the immune system.
Thus, the delayed-type hypersensitivity reaction has significant significance. The basis of the hypersensitivity reaction mechanism is inflammation, which helps to stop the infection in the affected areas and create a healthy immunity.