The immune system is designed to protect and defend the body from foreign intruders (bacteria, viruses). You can think of it like a security system for your body. It contains several different types of cells, some of which function like "security guards" and are constantly on patrol looking for any foreign invaders. When they spot one, they take action, and eliminate the intruder. In lupus, for some reason and we don't know why, the immune system loses its ability to tell the difference between a foreign intruder and a person's own normal tissues and cells. So, in essence, the "Security Guards" make a mistake, and they mistakenly identify the person's own normal cells as foreign (antigens), and then take action to eliminate them. Part of their response is to bring antibodies to the site that then attach to antigens (anything that the immune system recognizes as non-self or foreign) and form immune complexes. These immune complexes help to set in motion a series of events that result in inflammation at the site. These immune complexes may travel through the circulation (blood) and lodge in distant tissues and cause inflammation there.