Th124 - Long-term Viral Presence in Monocytes Correlates with Dysregulation of Innate Immunity in Patients with Multisystem Inflammatory Syndrome in Children (MIS-C)

Abstract Text: MIS-C is a severe post-infectious complication of SARS-CoV-2, with a known pathogenic role of monocytes, yet mechanisms sustaining inflammation remain unclear. Genetic variants in the OAS/RNase L pathway, involved in viral double-stranded RNA (dsRNA) sensing and inflammatory modulation, was linked to MIS-C. We analyzed PBMCs, plasma, and RNA from MIS-C patients, using a multifaceted approach to study NLRP3 inflammasome activation, blood biomarkers, autoantibody profiling, transcriptomics, and proteomics.

PBMCs, plasma, and RNA samples from MIS-C patients were analyzed. PBMCs were stimulated with LPS and ATP, and inflammatory responses were quantified using ELISA, flow cytometry, and imaging flow xytometry. Type-I interferon signature was measured using qPCR. RNA-sequencing data were analyzed through bioinformatics pipelines, including gene set enrichment analysis, while proteomics data were processed using weighted gene co-expression network analysis.

We found a monocyte exhaustion phenotype, demonstrated by reduced inflammasome activation in response to stimuli and an associated lack of IL-1β secretion. Intriguingly, dsRNA was detected in monocytes from MIS-C patients even during follow-up, suggesting a long-lasting viral presence that could drive sustained immune activation. Blood biomarker profiling, bulk RNA-seq, and proteomic analyses revealed a signature characterized by the activation of genes involved in antiviral response, systemic inflammation, oxidative stress, and coagulation pathways. Additionally, we observed anti-IL1RA autoantibodies in 40-50% of patients, consistent with previous reports.

Our findings highlight immune dysregulation in MIS-C, characterized by monocyte exhaustion, intramonocytic dsRNA persistence, autoantibodies, and distinct transcriptomic/proteomic signatures. These insights provide a deeper understanding of mechanisms underpinning sustained inflammation in post-COVID syndromes.