Recently, a second initiation mechanism of the alternative activation pathway was described, termed the properdin pathway [52] . Properdin is capable of recognizing several DAMPs and PAMPs on foreign and apoptotic cells, thus allowing C3 convertase assembly on the target surface [32, 52] . Properdin also functions as a stabilizer for C3 convertase complexes of the alternative pathway. In addition to properdin, a fifth complement activation pathway has been described, which identified the clotting factor thrombin as a C5 convertase. This notion was supported by the observation that thrombin is capable of generating C5a in the absence of C3, thus providing a direct link between the complement and coagulation system [53, 54] .