| Type III hypersensitivity | |
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| Classification and external resources | |
Immune complex |
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| MeSH | D007105 |
Type III hypersensitivity occurs when antigens and antibodies (IgG or IgM)[1] are present in roughly equal amounts, causing extensive cross-linking.
Type III hypersensitivity occurs when there is little antibody and an excess of antigen, leading to small immune complexes being formed that do not fix complement and are not cleared from the circulation. It is characterized by solvent antigens that are not bound to cell surfaces (which is the case in type II hypersensitivity). When these antigens bind antibodies, immune complexes of different sizes form[2]. Large complexes can be cleared by macrophages but they have difficulty binding to small immune complexes for clearance. These immune complexes insert themselves into small blood vessels, joints, and glomeruli, causing symptoms.
They deposit in tissues and induce an inflammatory response,[3] and can cause damage wherever they precipitate.
The reaction can take hours, days, or even weeks to develop.
Some clinical examples:
| Disease | Target antigen | Main effects | |
|---|---|---|---|
| Systemic lupus erythematosus | Nuclear antigens |
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| Post-streptococcal glomerulonephritis | Streptococcal cell wall antigens |
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| Polyarteritis nodosa | Hepatitis B virus antigen |
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| Reactive arthritis | Several bacterial antigens |
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| Serum sickness | Various |
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| Arthus reaction | Various |
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| Unless else specified in boxes, then ref is: [4] | |||
Other examples are:
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