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16th February 2024
Hypersensitivity Reactions
Summary
Hypersensitivity refers to an exaggerated systemic response from an otherwise normal immune system. Gell and Coomb’s classification categorises hypersensitivity reactions based on the cellular mechanism.
| Type | Mechanism | Pathology |
|---|---|---|
| I
Anaphylactic |
Immediate reaction
Antigen binds to IgE receptors on a mast cell, causing it to degranulate and release histamine and other vasoactive substances. |
Anaphylaxis
Atopy Drug reactions |
| II
Cytotoxic |
Antigen binds to the surface of IgG and IgM and activates complement, cell lysis and killer cells. | Autoimmune haemolytic anaemia
Goodpasture Syndrome Grave’s disease Blood transfusion reactions Idiopathic thrombocytopenic purpura Myasthenia gravis |
| III
Immune-complex |
Antigen and antibody combine to form a free-moving complex, which then migrates to the tissues where complement is activated. | SLE
Rheumatoid arthritis Serum sickness Post-streptococcal glomerulonephritis Syphilis Reactive arthritis Hypersensitivity pneumonitis |
| IV
Delayed hypersensitivity |
Antigens stimulating T lymphocytes causing lymphokine release | Contact dermatitis
Tuberculin skin reactions Graft rejection Graft vs. host disease Tuberculoid leprosy |
References
- Virella G (2019). Chapter 2 Overview of hypersensitivity. Medical Immunology (7th ed) CRC Press
- Feather A, Randall A, Waterhouse M (2020). Kumar and Clark’s Clinical Medicine (10th ed). Elsevier
- Manole C et al (2011). Manifestations of Systemic Lupus Erythematosus. Maedica: A Journal of Clinical Medicine 6 (4): 330 – 336
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