Immune profile of children diagnosed with multisystem inflammatory syndrome associated with SARS-CoV-2 infection (MIS-C).

Introduction: The pathophysiology of multisystem inflammatory syndrome associated with SARS-CoV-2 infection (MIS-C) remains poorly understood. This study aimed to define peripheral blood immune features in patients with MIS-C.

Material and methods: We analyzed seven children diagnosed with MIS-C between April 1 and May 15, 2021, in St. Joseph's Children's Hospital in Poznan (Poland).

Results: All patients had elevated inflammatory markers, IgG antibodies against SARS-CoV-2, and lymphopenia with a marked decrease in CD4+ and CD8+ T cells. The majority of CD4+ T cells were naive cells. Almost all (6/7) of the analyzed patients had a higher CD4+/CD8+ T cell ratio than average values. B cells were within the normal range - the majority were non-memory cells.

Conclusions: Children with MIS-C do not resemble adults during COVID-19 recovery. The immune profile of the studied patients differs from that of children with Kawasaki disease (KD), but it is similar to that of adults with severe COVID-19. The proposed explanation is a profound lymphopenia caused by SARS-CoV-2 infection - which persists for weeks - as a result leading to uncontrolled inflammation. In COVID-19 patients the T cell level returns to normal after the second week of the disease. Our data suggest that in children prolonged lymphopenia after COVID-19 can be a practical marker for possible MIS-C alert. If there is a continuum from lymphopenia to MIS-C, there is room for screening and prevention. Further studies are needed to determine whether steroid treatment introduced in a child with prolonged lymphopenia could stop the inflammatory process.