What classifies a disease as "auto-immune"?

A disease is classified as "auto-immune" when the body's immune system mistakenly targets and attacks its own healthy cells and tissues. In autoimmune diseases, the body's defense mechanisms, which are designed to protect against foreign invaders like bacteria and viruses, become misdirected and instead harm the body's own structures. This can lead to a wide range of symptoms and can affect various organs or systems within the body, depending on the specific condition.

Other options describe different aspects of immune function but do not align with the characteristics of autoimmune diseases. For instance, producing excess antibodies against infections typically represents a robust immune response, rather than malfunctional behavior seen in autoimmunity. A reduced immune response would point to an immunodeficiency rather than an autoimmune condition, where the immune system is active but targeting self-tissue instead. Lastly, complete inactivity of the immune system relates to severe immunosuppression or failure, which is distinct from the mistaken targeting seen in autoimmunity. Thus, the first choice accurately reflects the defining feature of autoimmune diseases.