COVID-19–associated multisystem inflammatory syndrome in children (MIS-C): A novel disease that mimics toxic shock syndrome—the superantigen hypothesis
Authors: Magali Noval Rivas, Rebecca A. Porritt, Mary Hongying Cheng, Ivet Bahar, Moshe Arditi
Journal: Journal of Allergy and Clinical Immunology (2020)

As of mid-September, the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected more than 30 million people, resulting in approximately 1 million deaths worldwide, including more than 200,000 deaths in the United States alone. Fever, dry cough, breathing difficulties, and gastrointestinal (GI) symptoms are typical features of coronavirus disease-2019 (COVID-19). Although 80% of infected people develop a mild disease, approximately 20% progress to severe COVID-19, which is associated with lung damage and breathing difficulties, and may lead to respiratory failure and death. Exacerbation of the COVID-19 immune response manifested by extensive cytokines release, called cytokine storm, may lead to multisystem inflammatory syndrome, which is fatal in 28% of cases.1Tay M.Z. Poh C.M. Rénia L. MacAry P.A. Ng L.F.P. The trinity of COVID-19: immunity, inflammation and intervention.Nat Rev Immunol. 2020; 20: 363-374Crossref PubMed Scopus (2942) Google Scholar Children can also be infected with SARS-CoV-2 (<2%); however, most confirmed pediatric cases have a less severe outcome and milder symptoms. In late April 2020, reports from Europe described the emergence of a new febrile pediatric entity that involved persistent fever, systemic hyperinflammation, multiorgan involvement with prominent and severe GI symptoms, and cardiogenic shock and hypotension, requiring pediatric intensive care unit care in most cases. Some who developed this syndrome, referred to as COVID-19–associated multisystem inflammatory syndrome in children (MIS-C), also demonstrated clinical findings including erythematous rashes, conjunctivitis, and inflammatory changes in the oral mucosa, features reminiscent of Kawasaki disease (KD). However, although initially designated as "Kawasaki-like," it soon became clear that this novel syndrome was very different from KD or KD shock syndrome, because MIS-C affected different demographics, and the clinical and laboratory parameters differed greatly between the 3 conditions2Whittaker E. Bamford A. Kenny J. Kaforou M. Jones C.E. Shah P. et al.Clinical characteristics of 58 children with a pediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2.JAMA. 2020; 324: 259-269Crossref PubMed Scopus (1425) Google Scholar (Table I). Although early research suggested that KD might be triggered by a superantigen (SAg), subsequent studies could not confirm Vβ2 family T-cell repertoire skewing in patients with KD. In contrast, MIS-C is more reminiscent of toxic shock syndrome (TSS).3Cheung E.W. Zachariah P. Gorelik M. Boneparth A. Kernie S.G. Orange J.S. et al.Multisystem inflammatory syndrome related to COVID-19 in previously healthy children and adolescents in New York City.JAMA. 2020; 324: 294-296Crossref PubMed Scopus (434) Google Scholar MIS-C cases reported from London showed similar findings, including an association with COVID-19 infection, higher incidence in children with African ancestry, and disease presentation with prominent features of shock, myocarditis, and severe GI symptoms, which are all very rare in KD.2Whittaker E. Bamford A. Kenny J. Kaforou M. Jones C.E. Shah P. et al.Clinical characteristics of 58 children with a pediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2.JAMA. 2020; 324: 259-269Crossref PubMed Scopus (1425) Google Scholar In addition, the overall clinical picture of MIS-C is similar in many respects to the late, severe COVID-19 phase in adults, which is characterized by a cytokine storm, hyperinflammation, and multiorgan damage, and often includes severe myocarditis and acute kidney injury, and laboratory and clinical features of TSS.4Pain C.E. Felsenstein S. Cleary G. Mayell S. Conrad K. Harave S. et al.Novel paediatric presentation of COVID-19 with ARDS and cytokine storm syndrome without respiratory symptoms.Lancet Rheumatol. 2020; 2: e376-e379Abstract Full Text Full Text PDF PubMed Scopus (44) Google ScholarTable IDemographic and clinical characteristics of patients with MIS-C, KD shock, TSS, and KDCharacteristicMIS-CTSSKD shock syndromeKDMedian age (y)9732EthnicityHispanic or Latino and Black, non-hispanicWhiteAsian and Asian ancestryAsian and Asian ancestryGI symptomsSevereSevereMildMildMyocardial dysfunction/cardiovascular shockYesYesYesNoNeuropsychological findings and CNS symptomsYesYesNoNoCoronary artery dilatation/aneurysmsTransient dilationNo real aneurysmTransient dilationNo aneurysmDilation and aneurysmsDilation and aneurysmsD-dimers levelsHighHighLowLowTroponin levelsHighNALowLowInflammation markers (ferritin, CRP, neutrophils)HighestHighestHigherHighLymphopeniaYesYesNoNoThrombocytopeniaYesYesNo∗Some cases of KD shock have been associated with thrombocytopenia. Table generated from Whittaker et al2 and Cheung et al.3NoResponse to IVIG and steroidsYesYesYesYesCNS, Central nervous system; CRP, C-reactive protein.∗ Some cases of KD shock have been associated with thrombocytopenia. Table generated from Whittaker et al2Whittaker E. Bamford A. Kenny J. Kaforou M. Jones C.E. Shah P. et al.Clinical characteristics of 58 children with a pediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2.JAMA. 2020; 324: 259-269Crossref PubMed Scopus (1425) Google Scholar and Cheung et al.3Cheung E.W. Zachariah P. Gorelik M. Boneparth A. Kernie S.G. Orange J.S. et al.Multisystem inflammatory syndrome related to COVID-19 in previously healthy children and adolescents in New York City.JAMA. 2020; 324: 294-296Crossref PubMed Scopus (434) Google Scholar Open table in a new tab CNS, Central nervous system; CRP, C-reactive protein. A causal link between SARS-CoV-2 infection and MIS-C has not yet been clearly established; however, many patients with MIS-C were reportedly exposed to someone known or suspected to have COVID-19. Although only around a third of patients with MIS-C are positive for SARS-CoV-2 by PCR, a large majority are PCR-negative but positive serologically for SARS-CoV-2 antibodies and/or have a history of mild COVID-19 infection or exposure several weeks before presentation. Such timing suggests that MIS-C is a postinfectious disease or an immune or autoimmune disease. Moreover, the virus may still be present in the GI tract of these patients, because they demonstrate very severe GI symptoms. Through structure-based computational modeling, we discovered that the SARS-CoV-2 spike protein encodes a high-affinity SAg-like sequence motif near the S1/S2 cleavage site of the spike protein. The region containing this motif exhibits a high affinity to bind to T-cell receptors (TCRs) by closely associating with the variable domains' complementarity-determining regions of both the α and β chains(Fig 1).5Cheng M.H. Zhang S. Porritt R.A. Noval Rivas M. Paschold L. Willscher E. et al.Superantigenic character of an insert unique to SARS-CoV-2 spike supported by skewed TCR repertoire in patients with hyperinflammation.Proc Natl Acad Sci U S A. 2020; 117: 25254-25262Crossref PubMed Scopus (219) Google Scholar,6Arad G. Levy R. Nasie I. Hillman D. Rotfogel Z. Barash U. et al.Binding of superantigen toxins into the CD28 homodimer interface is essential for induction of cytokine genes that mediate lethal shock.PLoS Biol. 2011; 9e1001149Crossref PubMed Scopus (117) Google Scholar Notably, this region (containing the SAg-like motif) is highly similar in sequence and 3-dimensional structure to a fragment of the superantigenic Staphylococcal Enterotoxin B (SEB), which is known to interact with the TCR and CD28.6Arad G. Levy R. Nasie I. Hillman D. Rotfogel Z. Barash U. et al.Binding of superantigen toxins into the CD28 homodimer interface is essential for induction of cytokine genes that mediate lethal shock.PLoS Biol. 2011; 9e1001149Crossref PubMed Scopus (117) Google Scholar SEB triggers large-scale T-cell activation and proliferation, resulting in massive production of a proinflammatory cytokine profile typical of TSS, similar to that which entails severity and death from COVID-19. Next-generation immunosequencing analysis of T-cell repertoires from patients with COVID-19 indicated that severe COVID-19 was associated with a TCRVβ skewing, enrichment of selected Vβ genes, and increased J diversity, consistent with SAg activity.5Cheng M.H. Zhang S. Porritt R.A. Noval Rivas M. Paschold L. Willscher E. et al.Superantigenic character of an insert unique to SARS-CoV-2 spike supported by skewed TCR repertoire in patients with hyperinflammation.Proc Natl Acad Sci U S A. 2020; 117: 25254-25262Crossref PubMed Scopus (219) Google Scholar These data support our hypothesis that MIS-C, as well as cytokine storm observed in adult patients with severe COVID-19, is mediated by SAg activity of the SARS-CoV-2 spike protein. Additional, prospective studies in adult and pediatric cohorts are warranted to test this hypothesis. Notably, both T and B cells can be triggered by SAgs to contribute to the innate immune response. Multiple autoantigenic immunoglobulins have been identified in children with MIS-C,7Consiglio CR, Cotugno N, Sardh F, Pou C, Amodio D, Rodriguez L, et al. The immunology of multisystem inflammatory syndrome in children with COVID-19. Cell 2020 Sep 6. https://doi.org/10.1016/j.cell.2020.09.016.Google Scholar raising the possibility that the SARS-CoV-2 SAg-like structure we identified may also possess B-cell SAg-like function. Furthermore, T-cell SAgs can interact with MHCII expressed on B cells to induce B-cell signaling pathways.8Morio T. Geha R.S. Chatila T.A. Engagement of MHC class II molecules by staphylococcal superantigens activates src-type protein tyrosine kinases.Eur J Immunol. 1994; 24: 651-658Crossref PubMed Scopus (56) Google Scholar It will be important to explore this potential in future studies. Some children with MIS-C develop neurological symptoms,3Cheung E.W. Zachariah P. Gorelik M. Boneparth A. Kernie S.G. Orange J.S. et al.Multisystem inflammatory syndrome related to COVID-19 in previously healthy children and adolescents in New York City.JAMA. 2020; 324: 294-296Crossref PubMed Scopus (434) Google Scholar including headache, altered mental state, and confusion, and similar neurological complications are reported in adult patients with COVID-19.9Ellul M.A. Benjamin L. Singh B. Lant S. Michael B.D. Easton A. et al.Neurological associations of COVID-19.Lancet Neurol. 2020; 19: 767-783Abstract Full Text Full Text PDF PubMed Scopus (1412) Google Scholar The pathologic mechanisms leading to these symptoms remain unknown. Interestingly, SAg-induced TSS has been associated with long-term neuropsychologic deficits in adults, including cognitive decline,10Rosene K.A. Copass M.K. Kastner L.S. Nolan C.M. Eschenbach D.A. Persistent neuropsychological sequelae of toxic shock syndrome.Ann Intern Med. 1982; 96: 865-870Crossref PubMed Scopus (61) Google Scholar and we identified a homology between the SAg motif of SARS-CoV-2 and neurotoxin-like sequences that are able to bind the TCR.5Cheng M.H. Zhang S. Porritt R.A. Noval Rivas M. Paschold L. Willscher E. et al.Superantigenic character of an insert unique to SARS-CoV-2 spike supported by skewed TCR repertoire in patients with hyperinflammation.Proc Natl Acad Sci U S A. 2020; 117: 25254-25262Crossref PubMed Scopus (219) Google Scholar Notably, SARS-CoV-2 spike contains other neurotoxin-like motifs as well, including in particular the segment T299-Y351, which has been recently observed to be a highly cross-reactive epitope that triggers CD4+ T-cell response.5Cheng M.H. Zhang S. Porritt R.A. Noval Rivas M. Paschold L. Willscher E. et al.Superantigenic character of an insert unique to SARS-CoV-2 spike supported by skewed TCR repertoire in patients with hyperinflammation.Proc Natl Acad Sci U S A. 2020; 117: 25254-25262Crossref PubMed Scopus (219) Google Scholar It will be interesting to determine whether these neurotoxin-like sequences in the SARS-CoV-2 spike protein contribute to the neurological manifestations observed in children with MIS-C and adults with severe COVID-19. Why only a small fraction of SARS-CoV-2–infected children develop MIS-C remains unclear. It is possible that a poor initial antibody response to the virus in a subset of children fails to produce neutralizing antibodies, leading to immune enhancement following SARS-CoV-2 reexposure. Alternatively, some HLA types may be more permissive, and respond more robustly to certain viral antigenic structures.5Cheng M.H. Zhang S. Porritt R.A. Noval Rivas M. Paschold L. Willscher E. et al.Superantigenic character of an insert unique to SARS-CoV-2 spike supported by skewed TCR repertoire in patients with hyperinflammation.Proc Natl Acad Sci U S A. 2020; 117: 25254-25262Crossref PubMed Scopus (219) Google Scholar Indeed, among the reported cases from London,2Whittaker E. Bamford A. Kenny J. Kaforou M. Jones C.E. Shah P. et al.Clinical characteristics of 58 children with a pediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2.JAMA. 2020; 324: 259-269Crossref PubMed Scopus (1425) Google Scholar 50% of patients with MIS-C were of Afro-Caribbean descent, which suggests a possible genetic component for MIS-C susceptibility. Finally, our findings suggest that immunomodulatory therapeutic approaches used for TSS, such as intravenous immunoglobulin (IVIG) and steroids, may also be effective for MIS-C. Indeed, most patients with MIS-C respond well to IVIG (2 g/kg) and aspirin, with or without steroids.3Cheung E.W. Zachariah P. Gorelik M. Boneparth A. Kernie S.G. Orange J.S. et al.Multisystem inflammatory syndrome related to COVID-19 in previously healthy children and adolescents in New York City.JAMA. 2020; 324: 294-296Crossref PubMed Scopus (434) Google Scholar Given the structural similarities between SEB and the SARS-CoV-2 spike SAg motif,5Cheng M.H. Zhang S. Porritt R.A. Noval Rivas M. Paschold L. Willscher E. et al.Superantigenic character of an insert unique to SARS-CoV-2 spike supported by skewed TCR repertoire in patients with hyperinflammation.Proc Natl Acad Sci U S A. 2020; 117: 25254-25262Crossref PubMed Scopus (219) Google Scholar it is possible that antibodies within IVIG that neutralize SEB cross-react with the SARS-CoV-2 spike, which may in part explain the beneficial response of MIS-C cases to IVIG. In addition, in the mouse model of TSS, lethal SEB SAg challenge can be prevented by short peptide mimetics of the SAg motif.6Arad G. Levy R. Nasie I. Hillman D. Rotfogel Z. Barash U. et al.Binding of superantigen toxins into the CD28 homodimer interface is essential for induction of cytokine genes that mediate lethal shock.PLoS Biol. 2011; 9e1001149Crossref PubMed Scopus (117) Google Scholar Therefore, it would be important to investigate the therapeutic potential of peptide mimetics of SARS-CoV-2 spike SAg-like region in COVID-19–induced hyperinflammatory syndromes in future studies. Further elucidation of the parameters affecting the interaction between SARS-CoV-2 spike glycoprotein and immune cells will be necessary to design effective preventive and therapeutic interventions. We gratefully acknowledge support from the National Institutes of Health.