To identify the differentially regulated plasma factors depending on COVID-19 disease severity, 350 plasma factors (Supplementary Table S1) from 20 plasma samples (10 from 3 moderate patients and 10 from 5 severe patients) were screened by quantitative immunoassays using a total of 21 multiplex panels according to the manufacturers’ instructions via a multiplex assay service (Koma Biotech., Seoul, Republic of Korea). Four types of commercially available kits were used for measurement (Supplementary Table S1). The MILLIPLEX MAP Human Complement Magnetic Bead Panel 2 (Millipore, Burlington, MA, USA) included C1q, C3, C3b/iC3b, C4, complement factor B, complement factor H, and properdin. The MILLIPLEX MAP Human Sepsis Magnetic Bead Panel 3 (Millipore) included elastase 2, lactoferrin, NGAL, resistin, and thrombospondin-1. Magnetic Luminex Performance Assay multiplex kits (R&D Systems, Inc. Minneapolis, MN, USA) were used for TGF-β1-3. Magnetic Luminex Screening Assay multiplex kits (R&D systems, Inc.) included all the other factors measured in this study. Assay plates were read with a Luminex 100/200TM analyzer (ThermoFisher, Waltham, MA, USA). For quantification for each factor, the supplied standard proteins were used, and a standard curve was drawn by the best fit algorithm using MasterPlex QT 2010 software (MiraiBio, Hitachi, CA, USA). We used detection limit values of non-detected factors below the detection range (Supplementary Table S2). Based on the screening results, 191 plasma factors were selected for further studies (Supplementary Tables S3).
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