In the mid-1980s, Swiss physician René Flammer discovered an antigen within the mushroom that stimulates an autoimmune reaction causing the body's immune cells to consider its own red blood cells as foreign and attack them. Despite this, it was not until 1990 that guidebooks firmly warned against eating "P. involutus", and one Italian guidebook recommended it as edible in 1998. The relatively rare immunohemolytic syndrome occurs following the repeated ingestion of "Paxillus" mushrooms. Most commonly it arises when the person has ingested the mushroom for a long period of time, sometimes for many years, and has shown mild gastrointestinal symptoms on previous occasions. The "Paxillus" syndrome is better classed as a hypersensitivity reaction than a toxicological reaction as it is caused not by a genuinely poisonous substance but by the antigen in the mushroom. The antigen is still of unknown structure but it stimulates the formation of IgG antibodies in the blood serum. In the course of subsequent meals, antigen-antibody complexes are formed; these complexes attach to the surface of blood cells and eventually lead to their breakdown.