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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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Induction and Monitoring of Active Delayed Type Hypersensitivity (DTH) in Rats

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Dermal hypersensitivity reactions to imported fire ants.

R D deShazo, C Griffing, T H Kwan

The Journal of Allergy and Clinical Immunology

|December 1, 1984

Summary

Over half of New Orleans residents stung by imported fire ants (IFA) experienced prolonged, distinct skin reactions. Standard skin tests may not detect this common insect hypersensitivity.

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Contact Hypersensitivity as a Murine Model of Allergic Contact Dermatitis

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Published on: September 26, 2022

Area of Science:

Entomology
Dermatology
Allergy and Immunology

Background:

Imported fire ants (IFA) are a common nuisance, with many individuals experiencing stings annually.
Previous research documented immediate wheal-and-flare reactions to IFA stings.
A significant portion of IFA-stung individuals exhibit atypical, persistent dermal reactions.

Purpose of the Study:

To investigate the characteristics of delayed dermal reactions to imported fire ant stings.
To compare these reactions with immediate hypersensitivity responses.
To evaluate the efficacy of standard skin testing for diagnosing IFA hypersensitivity.

Main Methods:

Survey of suburban New Orleans residents regarding IFA sting incidence and reactions.
Controlled sting experiments with live IFA on human volunteers.
Intradermal skin testing using IFA whole-body extract.
Biopsy analysis of sting reaction sites at 6 hours post-sting.

Main Results:

58% of surveyed residents reported IFA stings in the past year.
Over half of stung individuals developed persistent, pruritic, edematous lesions with pustules lasting over 24 hours.
Controlled stings and intradermal testing revealed that only 4 of 9 subjects with persistent reactions showed positive results.
Biopsies indicated "late phase reactions" with fibrin deposits and eosinophils in pustules of those with persistent reactions.

Conclusions:

Late-phase reactions are common following imported fire ant stings.
These reactions differ significantly from immediate wheal-and-flare responses.
Standard skin testing with IFA whole-body extract may be insufficient for diagnosing this prevalent form of insect hypersensitivity.