Haptoglobin: Proteins and Enzymes

Haptoglobin is an acute phase glycoprotein that is an inactive member of the peptidase S1 family of serine proteases. It is secreted by multiple cell types and binds with high affinity to circulating Hemoglobin. Association of Haptoglobin with free Hemoglobin protects tissues from Hemoglobin-mediated oxidative damage and facilitates Hemoglobin clearance. In addition, Haptoglobin has anti-inflammatory properties that are independent of Hemoglobin binding. It inhibits prostaglandin synthesis, scavenges nitric oxide, dampens the inflammatory response to endotoxins, and inhibits T cell proliferation and neutrophil respiratory bursts. Deletion of Haptoglobin in mice facilitates the development of autoimmune inflammation.