The Neonatal Liver as a Gateway for Echovirus Disease: Tropism and Antiviral Immune

Abstract

Neonatal susceptibility to enteroviral infection remains incompletely understood, despite the disproportionate morbidity and mortality associated with early-life disease. Echoviruses are a major cause of severe neonatal illness and can lead to rapid, fatal outcomes within the first weeks of life. Although acute hepatitis is a hallmark of severe echovirus infection, it remains unclear whether the liver is merely an outcome of systemic infection or a central gateway that precedes viral dissemination and disease outcome. This uncertainty has limited mechanistic understanding of why only a subset of infected neonates progress to lethal disease.Neonatal antiviral defense relies predominantly on innate immune responses since adaptive immunity is immature this early in life. The liver occupies a unique immunological position as both a metabolic organ and a pseudo–barrier site, yet its role in shaping neonatal susceptibility to enterovirus infection is poorly defined. Prevailing models of hepatotropic viruses emphasize type III interferons (IFNs) as dominant antiviral mediators at barrier sites, including the liver, in contrast, prior work from our lab has implicated type I IFNs in restricting echovirus dissemination from the gastrointestinal tract. The interplay of these interferon systems within the neonatal liver during echovirus infection remains unresolved. To address these questions, we leveraged a panel of neonatal, interferon knockout, transgenic mouse models to recapitulate the population most severely affected by echovirus infection. We performed single-cell RNA sequencing to define infection-induced changes in cellular composition and antiviral signaling at single-cell resolution from infected and uninfected livers across this panel. These approaches were complemented by microscopy and cell culture-based assays to validate virus-cell type colocalization and to confirm productive viral replication within the liver. Using these integrated approaches, we demonstrate that type I interferon signaling, but not type III interferon signaling, is essential for protection against echovirus infection, even at low challenge doses. We further identify Kupffer cells, a subset of dendritic cells, and, to a lesser extent, neutrophils as the principal producers of type I interferons in the infected neonatal liver. Critically, we show that hepatocyte-intrinsic responsiveness to type I interferons is required for survival, as selective disruption of type I interferon signaling in hepatocytes alone is sufficient to permit fatal infection. Together, these findings establish the neonatal liver as a central gateway that governs echovirus tropism, antiviral immune responses, and disease outcome. By redefining the interferon circuitry that protects the neonatal liver in early life, this work provides a mechanistic framework for understanding lethal enterovirus disease in neonates and identifies liver-intrinsic antiviral responses as key determinants of survival.