Complementopathies.

The complement system is an essential part of the innate immune system that requires careful regulation to ensure responses are appropriately directed against harmful pathogens, while preventing collateral damage to normal host cells and tissues. While deficiency in some components of the complement pathway is associated with increased susceptibility to certain infections, it has also become clear that inappropriate activation of complement is an important contributor to human disease. A number of hematologic disorders are driven by complement, and these disorders may be termed "complementopathies". This includes paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), cold agglutinin disease (CAD) and other related disorders, which will be the focus of this review. A better understanding of the central role of the complement system in the pathophysiology of these disorders may allow for application of therapies directed at blocking the complement cascade.