Sanne Hoeks

Restrained inflammation and neonatal WMI in viral encephalitis 61 5 INTRODUCTION Viral infections of the central nervous system (CNS) in neonates are associated with seizures and cerebral white matter injury, 1-4 which is a strong predictor of neurodevelopmental impairment. 5, 6 Enterovirus (EV), Human Parechovirus (HPeV) and Herpes Simplex virus (HSV) are common causes of neonatal viral encephalitis and can be associatedwith severewhitematter injury, 7-10 while pathophysiological mechanisms remain unclear. 8 In vitro and animal studies show that activated immune cells and soluble proteins in viral CNS infections contribute to neuropathology and induce long-term cellular damage or death. 11-14 Especially neonates suffer from severe clinical symptoms and possibly experience long-term consequences after neonatal viral encephalitis. The neonatal period is characterized by important processes of brain growth and maturation. The neonate encounters a pathogen in a period of critical brain development, especially for white matter structures that induces susceptibility for injury. 15 Furthermore, the neonatal immune system is equippedwith age-specific characteristics that reflect adaptation to the specific demands placed on the immune system in early life. 16, 17 Neonatal immune responses are generally dampened compared to adults and more potent inflammatory responses develop only gradually during the first year. 18, 19 Moreover, pathogens continuously evolve mechanisms to evade or inhibit the immune system and might even hijack immune mechanisms to facilitate infection and survival. 16 For example, fetuses and newborns are most severely affected by the ZIKA virus since it activates autophagy in neural stem cells, which in turn inhibits normal neurogenesis during development. 20 Based on these properties, pathogen-host interactions in neonates are supposed to be different from adults and might explain differences in clinical symptoms and long-term consequences after neonatal viral encephalitis. However, ethical and practical issues in studies on human newborns hamper experiments to address their state of immunity and potential connectionwith neuropathology. With the emergence of innovative technology, it is possible to simultaneously investigate a broad spectrum of immune proteins in minimal amounts of bodily fluids and therefore these methods are especially suitable for neonates. Soluble proteins produced by immune cells and by the local tissue of the inflamed brain tissue and endothelium, mediate inflammatory processes by activating and recruiting immune cells and therefore play key roles in the regulation of the immune response. Detection of these proteins in both cerebral spinal fluid (CSF) and in blood might serve as a biomarker to assess disease severity and may predict long-term neurological consequences. In this retrospective study, we aim to evaluate neonatal immune responses, cerebral injury and subsequent neurodevelopmental outcome in neonatal viral encephalitis. Therefore, we assessed a broad panel of 33 soluble immune-related proteins in CSF and plasma of neonates diagnosed with a viral encephalitis caused by EV, HPeV or HSV. Magnetic resonance imaging (MRI) of the brain and long-term neurodevelopmental follow-up data were used to categorize the impact of abnormalities on neurological development.