Hypersensitivity of the delayed type: the mechanism of development

The change in susceptibility or reactivity of an organism to a foreign substance is called an allergy (from the Greek "reaction to someone else's"). The name "allergy" was invented by the Austrian scientist Clemens Pirke in 1906. He also suggested using the term to describe the effect on the body of various factors from the external environment, and the substances that excite these allergic reactions, called allergens.

American Allergist R. A. Cook in 1947 created the first classification of allergies. By definition, there is an immediate type of hypersensitivity and delayed-type hypersensitivity. The latter type will be discussed in detail in this article. What is important, hypersensitivity reactions of immediate and delayed type differ significantly from each other.

The main difference

Hypersensitivity of the immediate type is a reaction to an antigen occurring 20-25 minutes after a secondary encounter with an allergen (antigen). A delayed-type hypersensitivity reaction Is expressed not earlier than 7-8 hours or several days. In 1968, PG Gell and RA Coombs wrote a scientific paper that was titled "A New Classification of Allergic Reactions." According to this classification, there are 4 main types of allergies.

Types of allergies

• Type 1 - anaphylactic, atopic, reactive. To manifestations of this type can be classified as edema Quincke, anaphylactic shock, atopic bronchial asthma, urticaria.
• 2 type - 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 in the etiology of serum sickness, rheumatoid arthritis, systemic lupus erythematosus. All these three types are closely related to haemagglutinin and belong to immediate type hypersensitivity .
• 4 type - hypersensitivity of delayed type, the mechanism of counteraction is characterized by cellular action of T-lymphocyte-heller antigen.

Sensitization

Hypersensitivity reaction of delayed type Is the sensitization of the organism to microbial antigens, bacteria, viruses, fungi, helminths, to artificial and natural antigens (chemicals, drugs), to individual proteins. Most clearly, hypersensitivity of the delayed type reacts to the introduction of low-immunogenic antigens. A small dose of antigens with subcutaneous injection causes delayed-type hypersensitivity. The mechanism of development An allergic reaction of this type is the hypersensitivity of T-lymphocytes-hellicans to antigens. заставляет выделяться вещества, например, интерлейкин-2, которые активизируют макрофаги, происходит гибель антигена, вызвавшего сенсибилизацию лимфоцитов. Hypersensitivity of lymphocytes causes substances, for example, interleukin-2, which activate macrophages, to release the antigen, which caused sensitization of lymphocytes. T-lymphocytes also include a protective mechanism in which bacteria, viruses or protozoa die.

This form of sensitization is seen in a variety of infectious diseases, such as tuberculosis, syphilis, brucellosis, diphtheria, mycoses, helminthiases and others, as well as graft rejection.

Example

The most obvious example of such reactions is the tuberculin test Mantoux. If a person with a tubercle bacillus is injected intradermally with tuberculin, 24-48 hours later an injection 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 monocyte-macrophage series.

Aneria

In rare cases, there is a lack of response. This is called anergy, that is, the lack of response of the body to stimuli.

аллерген, попадая в организм, гибнет. Positive energy occurs when the allergen gets into the body and dies. In this case, inflammation does not occur.

Negative energy occurs when the body can not 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, also it can be caused by increased activity of T-suppressors.

Parallergy and pseudoallergia

«парааллергия» и «псевдоаллергия». There are concepts of "allergy" and "pseudoallergia." при диагностировании инфекционных болезней, выражающихся аллергическими реакциями. They are found in the diagnosis of infectious diseases, which are allergic reactions.

Para - allergy is when the infected organism reacts to similar allergens, for example, infected with tuberculosis reacts to atypical mycobacteria.

Pseudoallergia is an allergy, for example, to tuberculin in a patient with leukemia.

Stages of allergy

In the allergic period, 3 stages are described:

1. Immunological stage. иммунной системы. At this stage, all the changes in the immune system occur . Entered into the body allergen combines with antibodies and hypersensitive lymphocytes.
2. The pathological stage. которые образуются в результате присоединения аллергена с антителами и гиперчувствительными лимфоцитами. At this stage, the cells produce mediators (biologically active chemicals), monokines, lymphokines, which are formed as a result of the attachment of the allergen with antibodies and hypersensitive lymphocytes.
3. Pathophysiological stage. At this stage, the clinic of the disease appears. It happens because the appeared mediators have a detrimental effect on the tissues of the body. At this stage, swelling, itching, spasms of smooth muscle tissue, circulatory disorders, etc. are observed.

These stages determine delayed-type hypersensitivity.

Treatment

This is one of the most difficult questions. Therapy should be performed distinctly from immediate-type hypersensitivity therapy, because delayed-type hypersensitivity is an immune inflammation.

Directivity

Treatment should be directed to the immunological moment, anti-inflammatory therapy and neutralization of the pathogen. And yet, therapy must begin with general rules for the treatment of allergic diseases. Be sure to observe a hypoallergenic diet. In the treatment of this type of hypersensitivity, etiologic treatment, that is, aimed at the cause of the disease, takes a special place.

Types of hypersensitivity of delayed type. Their treatment

This type of hypersensitivity is divided into contact, tuberculin and granulomatous, so treatment should be directed to a certain type.

• Contact hypersensitivity occurs when interacting with chemicals (cobalt, nickel, wood tar, mercury, etc.), drugs, poisonous plants. In addition to the basic treatment of allergies, in addition to the treatment of contact hypersensitivity, the termination of interaction with the causes of allergy, therapy aimed at the removal of inflammation, UV irradiation is appointed.
• Tuberculin hypersensitivity is related to diagnosis and is caused by tuberculin or similar antigens, so treatment does not require.
• Infectious hypersensitivity of delayed type occurs when sensitized to microorganisms that cause infectious diseases, such as: tuberculosis, syphilis, brucellosis, anthrax, gonorrhea, parasitic infestations. Treatment of infectious allergies is concentrated on the destruction of pathogens.
• Allergic hypersensitivity to soluble proteins occurs when the immune system weakens, in which the body does not take protein compounds such as milk, fish, eggs, nuts, legumes and some proteins contained in cereals. For effective treatment, all foods that cause allergies are excluded from the diet.
• Auto-allergic hypersensitivity is when sensitive tissues and own antibodies are produced on the body's own tissues, which cause allergies. There are two types of autoallergic allergy.

The first is when the immunity function is not damaged, but an autoallergen occurs, which causes a violation of immunity. The second is when immunity fails, not understanding where their proteins are, and where strangers, so he thinks that it is allergenic. Treatment is symptomatic and pathogenetic, which consists in the use of immunosuppressants. Basically it is corticosteroids.

Hypersensitivity to transplantation is the destruction of a foreign body implanted in the body. Prevent such an allergy by choosing the right donor, and by assigning various immunosuppressants to depress the immune system.

Thus, the delayed-type hypersensitivity reaction is of considerable significance. The mechanism of the hypersensitivity reaction is based on inflammation, which helps to stop infection in the affected areas and create healthy immunity.