Systemic lupus erythematosus

Systemic lupus erythematosus is a chronic autoimmune disease. Autoimmune means the body's defense system can no longer tell self from non-self: it loses what is called immune tolerance and starts making autoantibodies, that is, antibodies aimed at the person's own body. And chronic means it persists over time.

Much of the damage comes from what those antibodies set off once they latch onto their targets. They form immune complexes, which are clumps of antibodies bound to their targets, and those clumps deposit in the tissues. There they activate complement, a set of defense proteins that amplifies the response, and they recruit neutrophils, which are fast-acting white blood cells. The result at the site of deposition is inflammation. Think of clumps traveling through a pipe and lodging at different points: wherever one lodges, it leaves an inflamed area behind.

And because those complexes deposit in the tissues, lupus is not limited to a single organ. It can affect the skin, the joints, the kidneys, the blood, the lungs, the heart, the nervous system, and more. The word systemic in the name means exactly that.