hypersensitivity

synonym allergy (medical term) generally refers to hypersensitivity

This entry is made by Project of Compilation and Application of Scientific Terms in "Popular Science China" Encyclopedia to examine.

Hypersensitivity, that is, abnormal and excessive immune response 。 That is, the body and antigen Sexual substances interact under certain conditions to produce Sensitized lymphocyte or Specificity Antibodies, if combined with re entering antigens, can lead to physiological dysfunction and tissue damage Pathological reaction 。 also called allergy 。

Foreign name: hypersensitivity

Alias: hypersensitivity

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▪ Cause
▪ Autoimmune disease

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Hypersensitivity

Abnormal and excessive immune response 。 That is, the body and antigen Sexual substances interact under certain conditions to produce sensitized lymphocytes or Specificity Antibodies, if combined with re entering antigens, can lead to pathological immune response of physiological dysfunction and tissue damage. also called allergy 。 Hypersensitive antigenicity Matter is called allergen 。 It can be Complete antigen (Heterogeneous animal serum, histiocyte, microorganism parasite , plant pollen, animal fur, etc.), or Hapten (e.g penicillin 、 sulfa , phenacetin and other drugs, or low molecular substances such as lacquer). It can be exogenous or endogenous. The clinical manifestations of hypersensitivity are varied, which may be different due to the nature of allergens, ways of entering the body, participating factors, occurrence mechanism and individual reactivity.

The body appears an antibody (or cell) mediated immune scale for its own tissue components due to the destruction of its own stability Autoimmunity 。 Also called self allergy 。 This is a complex and multifactorial natural phenomenon. In addition to external influences (such as drug hapten and microbial infection), it is also closely related to the genetic factors of the body itself, especially those in major histocompatibility systems Immune response gene and Immunosuppression Gene abnormalities.

classification

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According to the speed of reaction, it can be divided into Immediate hypersensitivity And delayed type hypersensitivity. Gail and Combs classified hypersensitivity into the following four types:

Type I hypersensitivity reaction

Type I hypersensitivity reaction Also called anaphylaxis reaction (anaphylaxis) or Immediate hypersensitivity （immediate hypersensitivity）。 This type of hypersensitivity reaction is characterized by rapid reaction, rapid regression, obvious individual differences and genetic tendency, and generally only causes physiological dysfunction without serious tissue damage. because antigen Interact with antibodies (usually IgE, some IgG subclasses) on the medium releasing cells to make Fc of IgE on the cells be bridged by fiber, causing cell activation, and the membrane of intracellular particles fuse with the membrane to form a pipeline, so that some active media such as histamine, 5-hydroxytryptamine Slow reaction material -A (SPS-A), etc. These media can cause smooth muscle Shrinkage Telangiectasia , increased permeability and increased gland secretion. According to the action of these active substances Target cell Different, respiratory tract allergic reaction, digestive tract allergic reaction, skin allergic reaction or systemic allergic reaction may occur. The common type I hypersensitivity reaction is anaphylactic shock, which is caused by drugs drug eruption , food induced Allergic gastroenteritis , caused by pollen or dust rhinallergosis , bronchial asthma, etc.^[1]

Type II hypersensitivity reaction

Type II hypersensitivity reaction also called Cytolysis Type hypersensitivity reaction or cytotoxic type hypersensitivity reaction, after IgG or IgM antibodies combine with corresponding antigens on the surface of target cells NK cells It is involved in the pathological hypersensitivity reaction mainly caused by cell lysis or tissue damage. For example, the blood type does not match Transfusion reaction ， Hemolysis of newborn Both reaction and drug-induced hemolytic anemia belong to type II hypersensitivity reaction. Hyperthyroidism Graves disease is a special type II hypersensitivity reaction.

Type III hypersensitivity reaction

Type III hypersensitivity reaction also called Immune complex Type hypersensitivity or vasculitis type hypersensitivity. It is made of medium soluble antigen Antibody complex deposition to local or whole body Capillary basement membrane By activating complement and Basophil With the participation of neutrophils, it causes inflammatory reaction and tissue damage characterized by congestion and edema, local necrosis and neutrophil infiltration. Type III diseases include partial glomerulonephritis after streptococcal infection, Exogenous asthma Etc. Arthus reaction is a local type III hypersensitivity reaction. After repeatedly injecting antigen (such as hydrophobia vaccine 、 insulin ）After that, edema, hemorrhage and necrosis may occur locally inflammatory reaction 。^[1]

Type IV hypersensitivity reaction

Type IV hypersensitivity reaction It is also called delayed hypersensitivity reaction. It is a pathological manifestation mediated by immune cells. It is mediated by T cells. Common types are: chemicals (such as dyes) and skin protein binding Or change its composition to become antigen It can sensitize T cells. After re contacting the antigen, T cells become killer cell Or release Lymphokine cause Contact dermatitis 。 Another type is called Infectious allergy , which is caused by some pathogens antigenicity It is caused by stimulation, such as tuberculosis and syphilis. In addition, organ transplantation rejection, post vaccination encephalomyelitis, some Autoimmune disease They all belong to this type (see figure).

other

In addition to the above four types, some scholars have proposed Type V hypersensitivity (also known as stimulatory type allergy )。 Type VI hypersensitivity (also called antibody dependence Cytotoxicity Reaction), and even more types. Some allergen (such as penicillium) can also cause different types of hypersensitivity reactions in the same individual at the same time.

characteristic	Type I hypersensitivity	Type II hypersensitivity reaction	Type III hypersensitivity reaction	Type IV hypersensitivity reaction
antibody	IgE	IgG、IgM	IgG、IgM
antigen	Exogenous	cell surface	solubility	Intracellular
reaction time	15~30min	Min~hrs	3~8h	48~72h
Mediating factors	antibody	antibody	antibody	Tc
Histology	Mast cells, basophils, eosinophils	Antibodies and complements	Neutrophils and complement	Monocytes and lymphocytes
performance	Wind mass and flush	Cytolysis and necrosis	Erythema and edema	Erythema and Sclerosis

Autoimmunity

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Cause

The body appears antibody (or cell) mediated immunity against its own tissue components due to the destruction of its own stability. Also called self allergy. The reasons for its occurrence are: ① new antigen Or release the previously concealed isolation antigen, which is not tolerated by the immune system, and is generated once contacted (such as released due to trauma) immune response 。 As not formed before puberty sperm , new antigens formed after virus infection or malignant transformation; ② After some changes in the normal components of the body Antigenic determinant Caused by stimulating the immune system Autoimmunity 。 For example, the antibody is deformed and twisted due to its binding with antigen, exposing some amino acid Sequences (can be used as antigenic determinants) to stimulate the body to produce antibodies against its own components. Complement system The same can be said for some components in. Antibodies formed in this way can only be compared with deformed antibodies or complement Exposed determinants react. Rheumatoid arthritis The specific rheumatoid factor is targeted at the changed immunoglobulin Corresponding antibody of; ③ Due to cross reaction antigen Can also stimulate the body to produce immune response 。 These cross reactive antigens may have some antigenic determinants similar to their own components. For example, certain strains of streptococcus cause infection（ Rheumatic fever ）After that, you can find myocardium And endocardial antibodies.

Autoimmune disease

The above for itself immune response , without destroying the original self tolerance. Caused by the destruction of self tolerance Autoimmunity There are three types of diseases: ① self directed red blood cell antigen Autoimmune diseases caused by antibodies to determinant clusters, such as Autoimmune hemolytic anemia 。 The disease is characterized by destruction of red blood cells and anemia; ② Autoimmune disease caused by antibodies (such as thyroid antibody and gastric mucosal antibody) targeting specific tissue components of the body. The same patient may have multiple antibodies against tissues. It can be seen that the destructive diseases of these tissues and the presence of antibodies may not necessarily cause the disease. It is still uncertain whether antibody is the primary cause of these diseases; ③ By for multiple Animal tissue Autoimmune diseases caused by antibodies to common components (such as nucleic acids), such as Systemic lupus erythematosus 。

There are many hypotheses about autoimmunity, such as ① Taboo cloning According to the theory, because Immunocompetent cell Clone mutation or self stability disorder, and the forbidden strains that react to their own tissue components reappear; ② Autoantigen Cross reaction theory; ③ Hapten Function and autoantigen configuration change theory; ④ Inhibitory T cells Functional disorder theory, etc.

Autoimmunity It is a complex and multifactorial natural phenomenon. In addition to external influences (such as drug half antigen , microbial infection), but also closely related to the genetic factors of the body itself. In particular, it is possible to Immune response gene And (or) Immunosuppression Gene abnormalities.

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