Peripheral immunophenotypes in children with multisystem inflammatory syndrome associated with SARS-CoV-2 infection

Recent reports highlight a new clinical syndrome in children related to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)(1)-multisystem inflammatory syndrome in children (MIS-C)-which comprises multiorgan dysfunction and systemic inflammation(2-13). We performed peripheral leukocyte phenotyping in 25 children with MIS-C, in the acute (n = 23; worst illness within 72 h of admission), resolution (n = 14; clinical improvement) and convalescent (n = 10; first outpatient visit) phases of the illness and used samples from seven age-matched healthy controls for comparisons. Among the MIS-C cohort, 17 (68%) children were SARS-CoV-2 seropositive, suggesting previous SARS-CoV-2 infections(14,15), and these children had more severe disease. In the acute phase of MIS-C, we observed high levels of interleukin-1 beta (IL-1 beta), IL-6, IL-8, IL-10, IL-17, interferon-gamma and differential T and B cell subset lymphopenia. High CD64 expression on neutrophils and monocytes, and high HLA-DR expression on gamma delta and CD4(+)CCR7(+)T cells in the acute phase, suggested that these immune cell populations were activated. Antigen-presenting cells had low HLA-DR and CD86 expression, potentially indicative of impaired antigen presentation. These features normalized over the resolution and convalescence phases. Overall, MIS-C presents as an immunopathogenic illness(1)and appears distinct from Kawasaki disease. Characterization of a cohort of children with multisystem inflammatory syndrome associated with SARS-CoV-2 infection provides insights into the immunopathogenic features of the disease.