Figure 2.

The alternative complement pathway in health and disease. Factor D and the alternative complement pathway have been implicated in both healthy states and disease states. Under normal conditions, the pathway helps to protect against invading pathogens and maintain homeostasis and health of various tissues and organs. However, upon dysregulation, the alternative complement pathway can contribute to the pathogenesis of various diseases throughout the body. Although these diseases can affect specific organs or tissues (as indicated in the figure), many of them are also characterized by systemic complications and widespread inflammation. aHUS, atypical hemolytic uremic syndrome; ANCA-AV, anti-neutrophil cytoplasmic antibody–associated vasculitis; COVID-19, coronavirus disease 2019; C3G, complement 3 glomerulopathy; PNH, paroxysmal nocturnal hemoglobinuria.