The expression of proteins involved in Ig-mediated immune activation [e.g., Fc Gamma Receptor IIIa FCGR3A], proteins associated with heart failure [e.g., Tenascin C (TNC), Quiescin sulfhydryl oxidase 1 (QSOX1)], was enhanced in severe MIS-C compared to KD [39]. Here, FCGR3A is linked to COVID-19–associated multisystem inflammatory syndrome in children.