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How do autoantibodies damage healthy cells 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, the immune system mistakenly identifies healthy body components as foreign antigens, leading to the production of harmful autoantibodies. These autoantibodies damage healthy cells through several primary mechanisms:

Lysis and Phagocytosis: Autoantibodies bind to healthy cells, which can trigger the complement system—a series of proteins that create holes in cell membranes, causing them to burst (lysis). Alternatively, this binding can mark cells for ingestion by phagocytic cells, such as macrophages and neutrophils.123
Functional Interference: Autoantibodies can bind to cell receptors, either blocking normal signals or inappropriately stimulating them. For example, in Graves disease, autoantibodies bind to thyroid receptors, causing the gland to overproduce hormones.1
Immune Complex Deposition: Antibody-antigen combinations can circulate through the blood and lymph systems, eventually lodging in various tissues where they trigger destructive inflammatory responses.4

These processes reflect a failure in the body's self-regulatory mechanisms, which normally eliminate self-reactive lymphocytes before they can cause harm.14