Which of the following statements applies to chronic immune complex diseases?

• A. The immune system overreacts to the presence of an antigen.
• B. The immune system attacks the body's own cells.
• C. The immune system is depressed for a period of time following radiation therapy.
• D. There is an accumulation of antigen-antibody complexes in the bloodstream.

Answer: (D)

Chronic immune complex diseases arise when antigen–antibody complexes form in the circulation and accumulate in tissues, where they deposit and trigger inflammatory responses. These immune complexes activate complement and recruit inflammatory cells, leading to ongoing tissue inflammation and damage in organs such as the kidneys, joints, and blood vessels. That deposition and sustained presence of antigen–antibody complexes in the bloodstream is the hallmark described by this statement.

The other descriptions point to different immune phenomena: a general overreaction to an antigen describes broader hypersensitivity, not specifically immune complex–mediated disease; autoimmunity involves the immune system targeting the body's own cells, which is a different mechanism from immune complex deposition; and immunosuppression after radiation therapy reflects a temporary weakening of immune function rather than immune complex–driven pathology.