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How can immune complexes cause tissue damage in autoimmune diseases?
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immune system disorder
False-color scanning electron micrograph of a T cell infected with HIV (human immunodeficiency virus), the agent that causes AIDS (acquired immunodeficiency syndrome).
In autoimmune diseases, tissue damage occurs through a process known as Type III hypersensitivity, or immune-complex-mediated injury. This occurs when circulating antibodies (specifically IgG or IgM) bind to soluble antigensâwhich are not attached to cell surfacesâto form antigen-antibody complexes.12
When these complexes are deposited in tissues, particularly in the blood vessels, kidneys, joints, lungs, or skin, they trigger an inflammatory response. The mechanism of damage involves the following steps:134
- Complement Activation: The deposited immune complexes activate the complement system. This activation increases blood vessel permeability and releases potent pharmacological agents that attract inflammatory cells, such as granulocytes and macrophages, to the site of deposition.1452
- Enzymatic Destruction: These recruited cells release powerful enzymes intended to neutralize the complexes, but these enzymes also destroy local tissues, leading to inflammation and vessel damage.12
- Clinical Consequences: Depending on the site of deposition, this process results in various symptoms, such as the kidney damage seen in systemic lupus erythematosus, the joint inflammation characteristic of rheumatoid arthritis, or vasculitis.134