As described above the complement system plays a critical role in both innate and adaptive immune responses. Clearly pathogens go to great lengths to avoid complement activation. Deficiencies in complement proteins can lead to serious consequences resulting in diseases such as lupus, HUS, etc. On the other hand, excessive complement activation or dysregulated modulation may contribute to several diseases and pathological conditions such as multiple sclerosis (Ingram et al. 2009 ), Alzheimer's (Kolev et al. 2009 ), asthma (Wills-Karp 2007), COPD , sepsis (Ward 2008) , hyperacute organ rejection (Wasowska 2010) , etc. In sepsis, excessive C5a generation is thought to contribute to increased thymocyte apoptosis and consumptive coagulopathy, decreased innate immune functions of neutrophils, cardiomyopathy and multiple organ failure (for review, see Rittirsch et al. 2008b) .