CD4 and COVID-19: PBMCs obtained from 21 participants with MIS-C, 19 participants with convalescent COVID-19, and 20 HC were stimulated with CD4+ T cell MPs, equimolar volume of DMSO as a negative control, and phytohemagglutinin (PHA) as a positive control (gating strategy shown in Supplemental Figure 1A; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.155145DS1).