Onderzoek naar immunomodulerende strategieën bij flavivirale encefalitis

While the brain is arguably the most remarkable organ in the body, it is also highly vulnerable to infection and inflammation. To safeguard its function, it is protected by the skull and the blood-brain barrier (BBB), and operates within a tightly regulated immune environment. Nevertheless, neurotropic flaviviruses can overcome these defenses, establish infection and trigger brain inflammation, referred to as flaviviral encephalitis. This condition is associated with high morbidity, mortality and long-term neurological sequelae, driven not only by viral replication but also by excessive inflammation. Yet, no specific antivirals or validated therapies are available, with treatment remaining limited to supportive care. This thesis advances our understanding of (pathogenic) immune mechanisms involved in flaviviral encephalitis and explores the potential of immunomodulatory strategies to control disease severity. Here, we developed and characterized an immunocompetent mouse model of encephalitis using the neurotropic flavivirus Usutu virus (USUV). Following intracranial inoculation, mice exhibited viral replication in the brain, microglia activation, inflammatory cytokine production, leukocyte recruitment and BBB disruption, all hallmarks of viral encephalitis. Inflammatory monocytes were the most abundantly recruited leukocyte population in the brain following USUV infection, leading to the investigation of molecular mechanisms of their recruitment. Using CCR2-deficient mice, we demonstrated that monocyte recruitment (and to lesser extent, T cells) depends on the chemokine receptor CCR2, which is specifically required for their adherence to the vasculature and subsequent transmigration across the BBB. While blocking monocyte infiltration alone was not sufficient to achieve therapeutic benefits, CCR2 deficiency markedly reduced microglia activation and BBB disruption, highlighting CCR2 as a key contributor to neuroinflammation. IFN-γ-deficient mice displayed a similar but less pronounced phenotype, likely due to reduced cytokine production, particularly CCL2, and subsequent leukocyte recruitment. Effective treatment of viral infections in the CNS has proven difficult, mostly due to poor drug delivery across the BBB. In line with this, we showed that two promising antiviral compounds (favipiravir and NITD008) had no efficacy in the USUV mouse model. We therefore proposed that reducing immunopathology through immunomodulatory strategies represented a more feasible approach once CNS infection is established. Indeed, treatment with the glucocorticoid dexamethasone significantly attenuated USUV-induced neuroinflammation, reducing BBB disruption and clinical symptoms, despite an associated increase in viral titers. These results confirmed that excessive inflammation is a major driver of viral encephalitis severity. Combined strategies that limit both viral replication and restrain immune-mediated pathology may be a promising therapeutic approach for USUV encephalitis. Since infection-driven metabolic reprogramming supports both inflammatory responses and viral replication, we explored metabolic modulation as a potential dual strategy. Inhibition of glycolysis using 2-Deoxy-D-glucose reduced neuroinflammation and disease symptoms, but failed to restrict USUV replication. In contrast, sodium dichloroacetate, which counters metabolic reprogramming, lowered viral titers, yet showed no anti-inflammatory effect and yielded less clinical benefit. In summary, we propose that future therapies for flaviviral encephalitis will likely benefit from emphasizing anti-inflammatory approaches, while dual strategies targeting both inflammation and viral replication may offer added benefit once effective antivirals or optimized metabolic modulators become available.