Hypersensitivity refers to an abnormal adaptive immune response that occurs when the body is stimulated by certain antigens, physiological dysfunction or tissue cell damage. According to the mechanism and clinical characteristics of hypersensitivity reactions, it can be divided into four types: I, II, III and IV.
What are the characteristics of I, II, III, IV hypersensitivity reactions
Type I hypersensitivity reaction
IgE-mediated, mast cells, basophils, eosinophils and other release of biologically active mediators caused local or systemic reactions, rapid occurrence, rapid regression, often causing physiological dysfunction, a small number of tissue cell damage, with obvious individual differences and genetic predisposition.
Schematic diagram of the mechanism of occurrence of type I hypersensitivity reactions
Source: Medical Immunology, Ninth Edition of People's Medical Publishing House
Common clinical diseases: penicillin allergy, allergic rhinitis, allergic asthma, allergic gastroenteritis, urticaria, atopic dermatitis (eczema).
Type II hypersensitivity reaction
Pathological immune responses with cytolysis or tissue damage, mainly with the participation of complement, phagocytes, and NK cells, are caused by specific IgG or IgM antibodies against cell surface and extracellular matrix antigens, and occur more quickly.
Schematic diagram of the mechanism of occurrence of type II hypersensitivity reactions
Image source: Oncohema Key
Common clinical diseases: transfusion reactions, neonatal hemolysis, autoimmune hemolytic anemia, drug allergic hemocytopenia (penicillin can also be caused), Graves disease.
Type III hypersensitivity reaction
The inflammatory response and tissue damage characterized by congestion edema, local necrosis and neutrophil infiltration are caused by the participation of neutrophils, platelets, basophils and other effector cells with the participation of neutrophils, platelets, basophils and other effector cells after deposition of medium-sized soluble immune complexes deposited in local or systemic multiple capillary basement membranes throughout the body.
Schematic diagram of the mechanism of type III hypersensitivity reaction
Source: Medical Immunology, Ninth Edition of People's Medical Publishing House
Common clinical diseases: glomerulonephritis and serum disease caused by streptococcal infection.
Type IV hypersensitivity reaction
Effector T cell-mediated inflammatory immune response characterized by mononuclear cell infiltration by antigen stimulation. Type IV hypersensitivity is slower, also known as late-onset hypersensitivity. Usually occurs 24 to 72 hours after re-exposure to the antigen.
Schematic diagram of the mechanism of type IV hypersensitivity reaction
Source: Medical Immunology, Ninth Edition of People's Medical Publishing House
Common clinical conditions: tuberculosis, tuberculin test, contact dermatitis, rheumatoid arthritis mediated by Th1 and Th17, multiple sclerosis.
Table 1 Differences in type IV hypersensitivity reactions
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bibliography:
1. Cao Xuetao,Yao Zhi,Xiong Sidong,Si Chuanping,Yu Yizhi. Medical Immunology 7th Edition [M]. Beijing:People's Medical Publishing House,2018.07.]