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Related Concept Videos

Allergic Reactions: Anaphylaxis01:30

Allergic Reactions: Anaphylaxis

237
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,...
237
Allergic Reactions02:06

Allergic Reactions

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Overview
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Drug Toxicity: Allergic Reactions01:30

Drug Toxicity: Allergic Reactions

181
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...
181
Allergic Drug Reactions01:27

Allergic Drug Reactions

1.6K
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...
1.6K
Hypersensitivities01:30

Hypersensitivities

8.7K
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...
8.7K
Antibody Structure01:10

Antibody Structure

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Overview
Antibodies, also known as immunoglobulins (Ig), are essential players of the adaptive immune system. These antigen-binding proteins are produced by B cells and make up 20 percent of the total blood plasma by weight. In mammals, antibodies fall into five different classes, which each elicits a different biological response upon antigen binding.
The Y-Shaped Structure of Antibodies Consists of Four Polypeptide Chains
Antibodies consist of four polypeptide chains: two identical heavy...
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Related Experiment Video

Updated: Apr 17, 2026

Measuring Local Anaphylaxis in Mice
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C4a: An Anaphylatoxin in Name Only.

Scott R Barnum1

  • 1Departments of Microbiology and Neurobiology, University of Alabama at Birmingham, Birmingham, Ala., USA.

Journal of Innate Immunity
|February 10, 2015
PubMed
Summary

Complement activation generates C3a, C4a, and C5a. However, C4a lacks a receptor and clear function, suggesting it should not be classified as a complement anaphylatoxin alongside C3a and C5a.

Area of Science:

  • Immunology
  • Biochemistry

Background:

  • Complement activation produces three anaphylatoxins: C3a, C4a, and C5a.
  • C3a and C5a share inflammatory, developmental, and regenerative functions.
  • C4a's functional profile is uncertain due to potential contamination and lack of a known receptor.

Purpose of the Study:

  • To clarify the functional role of C4a within the complement system.
  • To determine if C4a should be classified as a true anaphylatoxin.

Main Methods:

  • Review of existing literature on anaphylatoxin function and receptor identification.
  • Analysis of functional data concerning C3a, C4a, and C5a.
  • Assessment of C4a receptor binding and signaling capabilities.

Main Results:

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  • C4a preparations are often contaminated with C3a and C5a, confounding functional studies.
  • No specific receptor for C4a has been identified.
  • C4a cannot signal through known C3a or C5a receptors.

Conclusions:

  • C4a lacks a defined receptor and distinct signaling pathway.
  • Evidence suggests C4a does not possess the functional characteristics of anaphylatoxins.
  • C4a should be excluded from the family of complement anaphylatoxins.