ARG1 and COVID-19–associated multisystem inflammatory syndrome in children: PCSK9 also exhibits a proinflammatory effect by promoting TNF-α expression while suppressing the anti-inflammatory markers ARG1 and IL-10.43 The beneficial effect of using PCSK9 inhibitors in adults with severe COVID-19 has been demonstrated44–46; however, elevated levels of this protein in MIS-C cases have not, to our knowledge, been previously reported.