RIG-I and TLR4 Responses and Adverse Outcomes in Pediatric Influenza-Related Critical Illness

Abstract Background Decreased tumor necrosis factor (TNF)-α production in whole blood following ex vivo lipopolysaccharide (LPS) stimulation indicates suppression of the toll-like receptor (TLR)4 pathway. This is associated with increased mortality in pediatric influenza critical illness. Whether anti-viral immune signaling pathways are also suppressed in these patients is unclear. Objectives We evaluated suppression of the TLR4 and the anti-viral retinoic acid-inducible gene-I (RIG-I) pathways with clinical outcomes in children with severe influenza infection. Methods In this 24-center, prospective, observational cohort study of children with confirmed influenza infection, blood was collected within 72 hours of intensive care unit admission. Ex vivo whole blood stimulations were performed with matched controls using the viral ligand, polyinosinic-polycytidylic acid (poly(I:C))-low molecular weight/LyoVecTM and LPS to evaluate interferon (IFN)-α and TNF-α production capacities (RIG-I and TLR4 pathways, respectively). Results Suppression of either IFNα or TNFα production capacity was associated with longer duration of mechanical ventilation and hospitalization, and increased organ dysfunction. Children with suppression of both RIG-I and TLR4 pathways (n=33/103, 32%) were more likely to have prolonged (≥7 days) multiple organ dysfunction syndrome (30.3% vs 8.6%, p=0.004) or prolonged hypoxic respiratory failure (39.4% vs 11.4% p=0.001) compared to those with single- or no pathway suppression. Conclusions Suppression of both RIG-I and TLR4 signaling pathways, essential for respective anti-viral and anti-bacterial pathogens responses, is common in previously immunocompetent children with influenza-related critical illness and is associated with bacterial co-infection and adverse outcomes. Prospective testing of both pathways may aid in risk-stratification and in immune monitoring.