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Hypersensitivity reactions form a cornerstone of immunological diseases and adverse reactions to medications, foods, and environmental agents. They are characterized by an exaggerated or inappropriate immune response to an antigen, leading to tissue damage and clinical symptoms. Understanding the various types of hypersensitivity reactions is pivotal for clinicians as they navigate diagnostic evaluations, patient management, and therapeutic interventions.
The ensuing table provides an in-depth look into the four classical types of hypersensitivity reactions: Type I (Immediate), Type II (Cytotoxic), Type III (Immune Complex), and Type IV (Delayed-Type). It incorporates current understanding from various sources, including the recent International Consensus on Anaphylaxis[1] and research findings from the National Center for Biotechnology Information (NCBI)
| Type of Hypersensitivity | Mechanism of Action | Immunoglobulin/Cell Type Involved | Clinical Examples | Additional Details |
|---|---|---|---|---|
| Type I (Immediate) | IgE-mediated release of antibodies, mast cell degranulation, histamine release | IgE | Allergic asthma, rhinitis, anaphylaxis, urticaria | Sensitization and effector stages; coordinated actions of B cells and T Helper Cells; immediate onset[17] |
| Type II (Cytotoxic) | Activation of complement system by IgG/IgM, cell damage/lysis | IgG, IgM | Hemolytic anaemia, thrombocytopenia, Goodpasture's syndrome | Uncommon; drugs or substances bind to surfaces of certain cell types; targeted by macrophages for clearance |
| Type III (Immune Complex) | Build-up of immune complexes,... |
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