Although C3 and C4 (Table 1, proteins 19 and 20 and Table 2, proteins 1 and 23) play a significant role in the innate immune system [15] a mouse model demonstrated that deficiency in C3 can be compensated by thrombin [41] and a genetically determined deficiency of C4 increases the risk for developing systemic lupus erythematosus [42]. Here, C3 is linked to systemic lupus erythematosus.