Serum Sickness

Serum sickness is a type III hypersensitivity reaction that occurs when the immune system responds to foreign proteins, historically animal-derived antiserum and now sometimes certain medications, by forming immune complexes that deposit in blood vessels and tissues. Symptoms typically appear one to two weeks after exposure and include fever, rash, joint pain and swollen lymph nodes, reflecting the inflammation triggered as the immune complexes activate the complement system. It was first described in patients who received horse-derived antitoxin for diseases such as diphtheria, and while classic serum sickness from animal antiserum is now uncommon, a similar serum sickness-like reaction can still follow certain drugs, including some antibiotics and biologic therapies. Treatment is generally supportive, with antihistamines, anti-inflammatory drugs or corticosteroids used to control symptoms, and the reaction typically resolves once the triggering substance is cleared from the body.