The observations described here, derived from computational analysis of SARS-CoV-2 sequence, structure and interactions, as well as RNA sequencing, TCR and BCR repertoire analysis, autoantibody arrays, and proteomics analysis performed on samples collected from MIS-C and COVID-19 patients, point towards a role for the SAg-like motif (residues E661-R685) we identified in SARS-CoV-2 spike in promoting hyperinflammation and potentially autoimmunity in PASC, including MIS-C and long COVID. Here, BCR is linked to COVID-19.