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Hypersensitivities

Hypersensitivities

Hypersensitivity, also known as a hypersensitivity reaction or allergic reaction, is a condition where the body's immune system reacts abnormally to a foreign substance. Such substances, that cause hypersensitivity are referred to as an allergen, could be something typically harmless to most people, like pollen or certain foods.
Types of Hypersensitivities
Hypersensitivity reactions are categorized into four types: Type 1, Type 2, Type 3, and Type 4. Each type has a distinct mechanism...

Hypersensitivity Reactions: Delayed Hypersensitivity Reactions

Hypersensitivity Reactions: Delayed Hypersensitivity Reactions

Delayed-Type Hypersensitivity (DTH), or Type IV hypersensitivity, is a cell-mediated immune response. It occurs when T cells, rather than antibodies, mediate a reaction to specific antigens. It is characterized by a delayed onset (1-2 days) and involves the recruitment of macrophages to the inflammation site.The initiation of a DTH response begins with the sensitization of T cells. During this phase, which lasts at least 1-2 weeks, antigen-specific T cells are activated, clonally expanded, and...

Drug Toxicity: Allergic Reactions

Drug Toxicity: Allergic Reactions

Drug-related allergies are immune-mediated responses triggered by the administration of pharmacological agents. These hypersensitivity reactions are classified based on the immune mechanisms involved. The four primary types—Type I, II, III, and IV—are mediated by different immunological pathways and exhibit distinct clinical manifestations.Type I Hypersensitivity/ IgE-Mediated Reactions: Immunoglobulin E (IgE) immediately mediates Type I hypersensitivity reactions. Upon initial exposure to a...

Allergic Reactions: Anaphylaxis

Allergic Reactions: Anaphylaxis

Anaphylaxis is a severe, life-threatening hypersensitivity reaction mediated by Immunoglobulin E (IgE) antibodies. When IgE binds to allergens, it triggers the release of mediators– histamine, leukotrienes, and prostaglandins from mast cells and basophils. These mediators cause vasodilation, edema, and inflammation, leading to various symptoms.The primary allergens causing anaphylaxis include food items (e.g., peanuts, shellfish), drugs (e.g., penicillin, asparaginase, corticotropin, heparin),...

Allergic Drug Reactions

Allergic Drug Reactions

Allergic reactions related to drugs are hypersensitivity responses driven by the immune system and bear no connection to the drug's therapeutic action. While drugs in isolation do not trigger an immune response, they can interact with endogenous proteins to form antigens. These antigens stimulate lymphocytes to produce antibodies. IgE-type antibodies attach themselves to mast cells. Upon subsequent exposure to the same stimulus, the antigen-antibody interaction is initiated, unleashing numerous...

Hypersensitivity Reactions: Immune-Complex Reactions

Hypersensitivity Reactions: Immune-Complex Reactions

Type III hypersensitivity reactions occur when antigen–antibody complexes form and activate the complement system. Normally, these complexes help the clearance of antigens by phagocytes and red blood cells. However, when large numbers of immune complexes are present, they can deposit in tissues—particularly in the walls of blood vessels—leading to inflammation and tissue injury. These deposits trigger complement activation and neutrophil recruitment, resulting in serum sickness, a systemic...

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Chapter 28: Classification of hypersensitivity reactions.

Ashraf Uzzaman, Seong H Cho

Allergy and Asthma Proceedings

|July 17, 2012

Summary

This summary is machine-generated.

The Gell and Coombs classification details four hypersensitivity reaction types based on immune response and injury mechanisms. This system has been refined to include subtypes like Type IIb and four distinct Type IV categories, offering a more precise understanding of immune-mediated diseases.

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Area of Science:

Immunology
Pathology

Background:

The Gell and Coombs classification is a foundational system for categorizing hypersensitivity reactions.
Understanding these reactions is crucial for diagnosing and treating various immune-mediated diseases.

Purpose of the Study:

To present the established Gell and Coombs classification of hypersensitivity reactions.
To detail the refined subtypes, particularly Type IIb and the four categories of Type IV hypersensitivity.

Main Methods:

Review and synthesis of the original Gell and Coombs classification.
Description of updated classifications including Type IIa, Type IIb, and the four subtypes of Type IV hypersensitivity (IVa, IVb, IVc, IVd).

Main Results:

The original classification includes Type I (IgE-mediated), Type II (cytotoxic), Type III (immune complex), and Type IV (T-cell mediated) hypersensitivity.
Refinements include Type IIb (antibody-mediated cell stimulating) and detailed subcategories of Type IV: IVa (Th1-mediated), IVb (Th2-mediated), IVc (cytotoxic T-cell mediated), and IVd (T-lymphocyte-driven neutrophilic inflammation).
Some diseases exhibit multiple types of hypersensitivity.

Conclusions:

The enhanced Gell and Coombs classification provides a more granular understanding of hypersensitivity reactions.
This detailed classification aids in the precise diagnosis and management of complex immune-related disorders.