While our data found a classical engagement of C3 with C3 and C4, nidogen-1 (NID1), and plasminogen (PLG), C3-LHF1 also engaged with other lupus- and autoimmune-related proteins, such as WDR1, RPL22, and PXDN (Appendix Fig. S3C), supporting its mechanism of interacting with surface binders. Here, C4A is linked to systemic lupus erythematosus.