Autoantibodies targeting thyroid tissue inhibit thyroid hormone production and induce chronic inflammation in the thyroid gland.

Study: Autoantibodies to selenoprotein P in chronic fatigue syndrome suggest selenium transport impairment and acquired resistance to thyroid hormone

This study found that certain antibodies in some people block selenium from reaching the thyroid, which stops the thyroid from making enough active hormone — causing symptoms like fatigue that look like an underactive thyroid. Even though the antibodies don’t attack the thyroid directly, they still cause the same harmful effects.

Study: Association of Anti-TPO Antibody and Inflammatory Markers with Thyroid Ultrasound Findings.

This study found that people with antibodies attacking their thyroid also had signs of inflammation and poor thyroid function, which means these antibodies likely cause both swelling and reduced hormone production in the thyroid.

Study: Resolution of Hashimoto thyroiditis with Janus kinase inhibitor therapy in a patient with alopecia universalis

This study showed that a drug that calms the immune system helped stop the body’s attack on the thyroid, which allowed the thyroid to start working normally again—proving that the immune system’s mistaken attack (via antibodies) was causing the damage.