Distinguishing immune activation and inflammatory signatures of multisystem inflammatory syndrome in children (MIS-C) versus hemophagocytic lymphohistiocytosis (HLH)

Background: Multisystem inflammatory syndrome in children (MIS-C) is a potentially life-threatening sequela of severe acute respiratory syndrome coronavirus 2 infection characterized by hyperinflammation and multiorgan dysfunction. Although hyperinflammation is a prominent manifestation of MIS-C, there is limited understanding of how the inflammatory state of MIS-C differs from that of well-characterized hyperinflammatory syndromes such as hemophagocytic lymphohistiocytosis (HLH).

Objectives: We sought to compare the qualitative and quantitative inflammatory profile differences between patients with MIS-C, coronavirus disease 2019, and HLH.

Methods: Clinical data abstraction from patient charts, T-cell immunophenotyping, and multiplex cytokine and chemokine profiling were performed for patients with MIS-C, patients with coronavirus disease 2019, and patients with HLH.

Results: We found that both patients with MIS-C and patients with HLH showed robust T-cell activation, markers of senescence, and exhaustion along with elevated T_H1 and proinflammatory cytokines such as IFN-γ, C-X-C motif chemokine ligand 9, and C-X-C motif chemokine ligand 10. In comparison, the amplitude of T-cell activation and the levels of cytokines/chemokines were higher in patients with HLH when compared with patients with MIS-C. Distinguishing inflammatory features of MIS-C included elevation in T_H2 inflammatory cytokines such as IL-4 and IL-13 and cytokine mediators of angiogenesis, vascular injury, and tissue repair such as vascular endothelial growth factor A and platelet-derived growth factor. Immune activation and hypercytokinemia in MIS-C resolved at follow-up. In addition, when these immune parameters were correlated with clinical parameters, CD8⁺ T-cell activation correlated with cardiac dysfunction parameters such as B-type natriuretic peptide and troponin and inversely correlated with platelet count.

Conclusions: Overall, this study characterizes unique and overlapping immunologic features that help to define the hyperinflammation associated with MIS-C versus HLH.