Schematic diagram summarizing clinical trials targeting different aspects of the complement system, registered on www.clinicaltrials.gov as of 3 September 2020. C3 with a cleaved thioester bond (ie, C3b or C3(H₂O)) binds factor B. Factor B is then cleaved by factor D to form C3bBb. Properdin (not shown) stabilizes this C3 convertase, which can cleave many molecules of C3 to C3b and thereby amplifies the AP. The factor D inhibitor tested in the paper by Yuan et al (ACH145951) is in purple and is not currently registered. Ag-Ab, antigen-antibody; C5aR, C5a receptor; CP, classical pathway; LP, lectin pathway; MASP, mannan binding lectin-associated serine proteases; rC1INH, recombinant C1-esterase inhibitor. Created with www.biorender.com. For additional information, see Figure 6 in the article by Yu et al that begins on page 2080.