Immune dysregulation and multisystem inflammatory syndrome in children (MIS-C) in individuals with haploinsufficiency of SOCS1

TLDR

SOCS1 is a key negative regulator of IFN signaling, and heterozygous loss‑of‑function mutations lead to heightened IFN responses and predispose to infection‑driven autoimmune cytopenias, as illustrated by two patients with immune thrombocytopenia and autoimmune hemolytic anemia during acute infections. The study aimed to uncover the mechanisms behind infection‑driven autoimmune cytopenias. Whole‑exome sequencing was performed on both patients, and the functional impact of the identified truncating SOCS1 variants was validated in their PBMCs. Both patients carried unique heterozygous truncating SOCS1 variants that caused increased STAT1 phosphorylation and an IFN‑stimulated transcriptional signature, and one patient’s SARS‑CoV‑2 infection triggered MIS‑C, linking SOCS1 loss to the hyperinflammatory state characteristic of MIS‑C.

Abstract

We studied 2 unrelated patients with immune thrombocytopenia and autoimmune hemolytic anemia in the setting of acute infections. One patient developed multisystem inflammatory syndrome in children in the setting of a severe acute respiratory syndrome coronavirus 2 infection. We sought to identify the mechanisms underlying the development of infection-driven autoimmune cytopenias. Whole-exome sequencing was performed on both patients, and the impact of the identified variants was validated by functional assays using the patients' PBMCs. Each patient was found to have a unique heterozygous truncation variant in suppressor of cytokine signaling 1 (SOCS1). SOCS1 is an essential negative regulator of type I and type II IFN signaling. The patients' PBMCs showed increased levels of signal transducer and activator of transcription 1 phosphorylation and a transcriptional signature characterized by increased expression of type I and type II IFN-stimulated genes and proapoptotic genes. The enhanced IFN signature exhibited by the patients' unstimulated PBMCs parallels the hyperinflammatory state associated with multisystem inflammatory syndrome in children, suggesting the contributions of SOCS1 in regulating the inflammatory response characteristic of multisystem inflammatory syndrome in children. Heterozygous loss-of-function SOCS1 mutations are associated with enhanced IFN signaling and increased immune cell activation, thereby predisposing to infection-associated autoimmune cytopenias.