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How does an autoimmune disease cause the immune system to attack healthy cells?

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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).

Autoimmunity occurs when the immune system fails to distinguish between foreign invaders and the body’s own healthy tissues, treating the latter as if they were harmful antigens. Normally, the body eliminates self-reactive lymphocytes before they mature, but this process can fail due to genetic, hormonal, or environmental factors.12

When this failure occurs, the immune system attacks healthy cells through several mechanisms:

Autoantibodies: B cells produce harmful antibodies that bind to healthy cells. This can trigger phagocytosis (ingestion), cause cells to burst (lysis), or interfere with normal cellular function, such as overstimulating hormone receptors.12
Cell-Mediated Attack: T cells may launch a direct assault on healthy tissues, leading to their destruction.13
Immune Complexes: Combinations of antibodies and antigens can circulate in the blood and lodge in various tissues, causing widespread damage and inflammation.1

These attacks may be triggered by cross-reactions, where infectious agents mimic self-antigens, or by the exposure of previously hidden self-antigens following injury or infection.1