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Allergic Reactions

Allergic Reactions

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...

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),...

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...

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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Updated: Jul 20, 2026

Basophil Activation Test for Allergy Diagnosis

Basophil Activation Test for Allergy Diagnosis

Published on: May 31, 2021

Defective histamine release in chronic urticaria.

F Kern, L M Lichtenstein

The Journal of Clinical Investigation

|May 1, 1976

Summary

Patients with chronic urticaria exhibit a defect in leukocyte histamine release, impacting their response to anti-human IgE. This finding suggests a desensitization-like phenomenon in these patients.

Area of Science:

Immunology
Dermatology
Cell Biology

Background:

Chronic urticaria is a common condition often associated with histamine release.
The exact mechanisms underlying histamine release defects in chronic urticaria are not fully understood.

Purpose of the Study:

To investigate histamine release from peripheral blood leukocytes in patients with chronic urticaria compared to nonatopic controls.
To identify potential defects in the histamine release pathway triggered by anti-human IgE.

Main Methods:

Leukocyte histamine release assays using varying concentrations of anti-human IgE.
Measurement of serum IgE levels and total leukocyte histamine content.
Passive sensitization, 125I-anti-IgE autoradiography, ionophore stimulation, and cyclic AMP level assessments.

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Main Results:

Patients with chronic urticaria showed significantly lower histamine release in response to anti-human IgE compared to controls.
Serum IgE levels were higher in patients, but total histamine content was similar.
Basophil histamine release was normal when stimulated by ionophore, and cyclic AMP levels were comparable between groups.

Conclusions:

Chronic urticaria patients possess a defect in leukocyte histamine release occurring after IgE-anti-IgE interaction but before the release stage.
This defect appears to be acquired and resembles desensitization, not a quantitative abnormality in IgE binding or basophil responsiveness.