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. 2023 Oct 6;14:1254948. doi: 10.3389/fimmu.2023.1254948

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Copyright © 2023 Bennike

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Overview of the complement system, with a focus on the three activation pathways: (A) The classical pathway which is activated by antibody-antigen complexes, (B) the lectin pathway which is activated on bacterial and viral surfaces, and (C) the alternative pathway which is continuously active. The pathways lead to the terminal pathway and formation of the membrane attack complex (MAC). The larger proteolytic fragment of C2 is in this review termed C2b by the recently recommended nomenclature for complement pathways which aligns C2 with the other complement factors (19). FCN, ficolin; MBL, mannan-binding lectin; MASP, mannan-binding lectin serine proteases (20).