Multi-system inflammatory syndrome in children (MIS-C) is a post-viral inflammatory vasculopathy of children and adolescents following Covid-19 infection. It affects one of 1000-5000 children. Latency between mild or asymptomatic Covid-19 infection and MIS-C is 4-6 weeks. The immune response in MIS-C seems to be dysregulated and different from that during acute SARS-CoV-2 infection. The investigators are planning to investigate the immune response in children with MIS-C. RNA and protein expression of cytokines and immune cell-related markers will be determined via multiplex ELISA, FACS, quantitative PCR, RNAseq, and Western blot. The use of highly sensitive multiplex methods will allow for the analysis of a large number of parameters in the smallest possible amount of sample. Sample preparation and analysis will be performed in close collaboration with the Centre for Molecular Medicine Cologne (CMMC) and the Institute of Virology. With this project the investigators hope to identify risk factors for developing MIS-C and extend the knowledge on therapeutic options for the treatment of this condition.