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"Maybe it's autoimmune."
―At some point in the series Lisa Cuddy, Robert Chase, Allison Cameron, Eric Foreman, Lawrence Kutner, Remy Hadley, James Wilson, Chris Taub, and Jeffrey Cole
"If someone says autoimmune, you're fired."
Gregory House

An autoimmune disease is any disease where the body's immune system is active against healthy cells. It covers a wide variety of ailments with different underlying causes, but the ailments share several symptoms and outcomes, making diagnosis of a particular cause difficult. Untreated autoimmune conditions will often lead to organ failure, either due to the immune system attacking the organs directly, or creating large quantities of toxic substances that poison the organs.

Some of the best known autoimmune diseases are:

  • Lupus - the show's most frequently mentioned disease, where the body's immune system mistakes healthy cells for foreign bodies.
  • Sepsis - where the immune system goes into overdrive against an infection, preventing the normal functioning of the body's organs.
  • Tissue rejection - where the body's immune system attacks a transplanted organ from another donor.
  • Celiac disease - where the body reacts to the gliadin in gluten by attacking the small intestine and wearing down the villi and therefore the intestinal mucosa to cause gastrointestinal symptoms and malnutrition, amongst other problems.

Autoimmune disease at Wikipedia