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16th February 2024
Autoimmune Systemic Disorders and Hypersensitivity Reactions
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
Autoimmune Systemic Disorders
Summary
Autoimmune conditions comprise a broad range of diseases caused by an inappropriate immune reaction to otherwise healthy human cells. The clinical course of the disease will depend on which cells are being targeted.
| Disorder | Symptoms | Target of autoantibody |
|---|---|---|
| Myasthenia gravis | Fatigable muscle weakness commonly involves the eye (ptosis) but can be more generalised. | Acetylcholine receptor |
| Pernicious anaemia | The inability to absorb B12 leads to macrocytic anaemia | Intrinsic factor, gastric parietal cells |
| Graves’ disease | Consistent with hyperthyroidism – weight loss, tremor, diarrhoea | TSH receptor |
| Hashimoto’s thyroiditis | Consistent with hypothyroidism – weight gain, constipation, fatigue | Thyroid peroxidase, Thyroglobulin |
| Goodpasture’s syndrome | Pulmonary haemorrhage, glomerulonephritis | Glomerular basement membrane |
| SLE | Various depending on the local site involved. Most commonly: constitutional symptoms, arthritis/arthralgia, Raynaud’s. Vasculitis, pericarditis, lupus nephritis | Double stranded DNA, ANA, Lupus anticoagulant |
| Rheumatoid arthritis | Symmetrical peripheral polyarthritis | Rheumatoid factor (IgG), Citrullinated peptide antibodies |
| Vasculitis | Various depending on the vessels involved | ANA, ANCA |
| Primary biliary cholangitis | Fatigue, pruritis, cholestatic LFTs, jaundice leading to liver cirrhosis | Mitochondria |
| Mixed connective tissue disorder | Overlapping features of systemic sclerosis, SLE and RA | Extractable nuclear antigens (ENA) |
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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