Children with MIS-C, vs those with acute COVID-19, had significantly elevated GM levels of C3 (318.2 [70.7] ng/mL vs 237.7 [61.8] ng/mL), C5a (2614.0 [336.2] ng/mL vs 1826.0 [541.0] ng/mL), and MBL (79.0 [12.4] ng/mL vs 69.6 [14.7] ng/mL) (Figure 1, Figure 2, eFigure 1 and eTable 2 in Supplement 1). Here, C3 is linked to COVID-19.