This study seeks to explore immunological mechanisms in patients with Multisystem Inflammatory Syndrome in Children (MIS-C) to improve the understanding of this pathogenesis of this disease.

In a cohort of MIS-C patients diagnosed during the Wild type, Alpha, Delta and Omicron waves, research samples will be analyzed for whole-blood RNA expression, proteomics, inflammatory cytokines, cellular immune populations, autoantibodies, as well as host genetic markers.

BACKGROUND Multisystem inflammatory syndrome in children (MIS-C) is a rare severe complication to SARS-CoV-2 infection in children. Thousands of children worldwide have been hospitalized with this new disease. Yet, the immunological mechanisms are sparsely described.

AIM The project seeks to explore immunological mechanisms in patients with MIS-C.

METHOD From a prospective nationwide cohort of patients with MIS-C from Denmark (May 2020-March 2022), research samples will be investigated for whole-blood RNA expression, proteomics, inflammatory cytokines, metabolomics, cellular immune populations, autoantibodies, as well as host genetic markers allowing for detailed mapping this disease. Samples from MIS-C patients will be compared to patients with bacterial and viral disease, and other inflammatory diseases.

TIME FRAME Sample identification: February 1 2022 to April 1, 2022. Sample analysis: April 1, 2022 to December 31, 2022

PERSPECTIVES New molecular-based tools may lead to improved understanding of the pathogenesis of MIS-C. This could form basis for development of novel diagnostic markers, identification of severe phenotype and therapeutic interventions.

Inclusion Criteria:

• Patients diagnosed with MIS-C, according to the CDC criteria aged 0-17 years

Exclusion Criteria:

• Patients from whom patient/parent/legal guardian signed consent is not received

Patients fulfilling the diagnostic critieria of MIS-C, according to the CDC