F12 and systemic lupus erythematosus: To explore functional roles of these pathways for SLE disease severity, several differentially expressed signaling proteins that were identified by our proteomic experiment were measured in lupus cohort II, including mannan-binding lectin-associated serine protease 2 (MASP2), C7, C1q, C4, coagulation factor 7 (F7), F9, F12, F13, fibrinogen (FIB), Von Willebrand factor (VWF), protein S (PPOS) and antithrombin-III (ATIII).