Serum C3 and C4 were determined by immunoturbidimetry (The Binding Site, San Diego, California, USA)11 (link) and were considered low if below the manufacturer’s lower limits of normal (81.1 and 12.9 mg/dL for C3 and C4, respectively). Low complement status refers to low C3 and/or low C4.
Complement activation was determined using CB-CAPs measured by quantitative flow cytometry.11 (link) CB-CAPs were considered abnormal if levels of EC4d and/or BC4d were above the 99th percentile of a group of healthy individuals (>14 and >60 net mean fluorescence intensity, respectively).7 8 11 (link) Abnormal CB-CAPs status refers to abnormal EC4d and/or abnormal BC4d.
Anti-double-stranded DNA (dsDNA) antibodies were determined by ELISA (Quanta Lite, Inova Diagnostics, San Diego, California, USA). All serum samples above 301 IU/mL were further tested by indirect immunofluorescence assay (IFA) using the Crithidia luciliae assay (Nova-Lite, Inova Diagnostics). Anti-dsDNA antibodies were considered positive if confirmed by IFA.
Complement activation was determined using CB-CAPs measured by quantitative flow cytometry.11 (link) CB-CAPs were considered abnormal if levels of EC4d and/or BC4d were above the 99th percentile of a group of healthy individuals (>14 and >60 net mean fluorescence intensity, respectively).7 8 11 (link) Abnormal CB-CAPs status refers to abnormal EC4d and/or abnormal BC4d.
Anti-double-stranded DNA (dsDNA) antibodies were determined by ELISA (Quanta Lite, Inova Diagnostics, San Diego, California, USA). All serum samples above 301 IU/mL were further tested by indirect immunofluorescence assay (IFA) using the Crithidia luciliae assay (Nova-Lite, Inova Diagnostics). Anti-dsDNA antibodies were considered positive if confirmed by IFA.
