Another vote, actually two, for the possibility of surgery causing SLE lupus. My Dad was 36 when he had surgery for a hernia and soon afterwards is body went to garbage and he was diagnosed a couple years later with SLE. I had surgery more than a year and a half ago to repair my severely dislocated shoulder and was under general anesthesia for two hours. Soon after starting physical therapy and rehab, my body went crashing to crap. I was diagnosed two to three weeks ago with SLE lupus and dermatomyositis (a mixed connective tissue disease). I was so weak and had lost the strength to move my legs out of bed in the morning and could not stand without assistence.
So, we've two votes for heredity being involved in SLE as well as surgery possibly being a stress trigger.