Three pathways of complement activation have been reported: antibody-dependent classical pathway, antibody-independent alternative pathway and lectin pathway. The activation of each pathway involves the formation of a serine protease complex, which leads to the activation of the central complement component C3. In the lectin pathway, mannose-binding lectin (MBL)-related serine protease (MASP) forms a complex with polylectin molecules involved in pattern recognition. After the recognition molecule binds to carbohydrates on the surface of the microorganism, MASP is converted to its active form and initiates complement activation. Three types of human MASP have been reported. MASP-1, MASP-2 and MASP-3. MASP-1 appears to cleave the second complement component C2, but not C4. The proteolytic activity of MASP-1 is inhibited by C1 inhibitors. In addition, MASP-1 has reactivity very similar to thrombin. MASP-1 can catalyze the formation of cross-linked fibrin. MASP-1 participates in the formation of cross-linked fibrin clots and leads to the release of chemokines, which represent the biological activity of MASP-1. Another splicing product of the MASP-1 gene is called MASP-3. MASP-1 is associated with smaller MBL oligomers, while MASP-3 is associated with larger oligomers. The substrate of MASP-3 is unknown. The antibody recognizes the heavy chain shared by MASP-1 and MASP-3.