c inflammation as shown by higher ferritin concentrations.2 However, in many aspects, COVID-19 does not resemble typical MAS. We propose that the cytokine storm syndrome seen in COVID-19 is dissimilar to that seen in canonical MAS and should be regarded as a distinct entity and approached in a novel way reflecting its unique qualities.

Cellular immunity and T-cell polarisation in COVID-19
Whereas virus-induced MAS shows the classic hallmarks of a T-helper (Th)-1 profile, with high production of IFNγ,1, 3 COVID-19 is instead characterised by circulating T cells that show an activated Th17 membrane phenotype (CD38+HLA-DR+CD4+CCR6+)4 and express granulocyte–macrophage colony-stimulating factor (GM-CSF) in part along with IFNγ.5 Concentrations of both I