Properdin Binds Pseudomnas aeruginosa and is Required for Neutrophil Extracellular Trap Mediated Activation of Complement Alternative Pathway

Neutrophils play an important, yet poorly understood role, in complement mediated pathologies. Here we identified that neutrophils contain key components from the complement alternative pathway: properdin (CFP), complement component 3 (C3), complement factor B (CFB), and complement factor H (CFH). Activation of neutrophils resulted in secretion of these complement components. When neutrophils are further activated to form neutrophil extracellular traps (NETs), CFP is deposited onto the surfaces of the NETs. In addition, CFP is able to bind to Pseudomonas aeruginosa, an opportunistic bacterium which can activate neutrophils to form NETs. Furthermore, NETs activate complement and increase formation of the terminal complement complex. The activation of complement on NETs can be initiated through multiple pathways, however, activation of the alternative pathway is dependent on CFP. This mechanism, potentially required for effective host defense, may also contribute to complement activation and disease.MAS