Complement system components and fragments

The complement system is a complex network of over 30 plasma and cell-surface proteins that play a critical role in the innate immune response. It functions through three primary pathways—classical, lectin, and alternative—which converge on the cleavage of C3 and subsequently C5, leading to the formation of the membrane attack complex (MAC) and the release of potent inflammatory mediators like C3a and C5a [1][2]. Dysregulation of these components is implicated in various rare and common diseases, including paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), and age-related macular degeneration [3][4]. Therapeutic strategies involve targeting specific fragments or enzymes within the cascade, such as C5 inhibitors (e.g., eculizumab) or C3 inhibitors (e.g., pegcetacoplan), to prevent tissue damage and hemolysis [5]. While highly effective, blocking these pathways significantly increases the risk of life-threatening infections by encapsulated bacteria, necessitating prophylactic vaccination [6].

Other names

Complement cascadeComplement proteinsComplement factorsComplement system