CD40-CD40L Interaction is Critical in Mounting Host Immunity Against M-Cov Mouse Hepatitis Virus Induced Neuroinflammatory Demyelination

Abstract Chronic progressive neuroinflammatory disease multiple sclerosis (MS) is characterized by loss of neuronal functions resulting from demyelination with or without axonal degeneration. Infiltration of T lymphocytes and activation of microglia and their interplay are the major pathophysiological events leading to neurodegeneration in MS. Our studies in Mouse Hepatitis Virus (MHV) induced neuroinflammatory model demonstrated a protective role of CNS infiltrating CD4+ T cells. In the absence of CD4+ T cells, microglial activation fails to resolve, and mice are more susceptible to acute poliomyelitis and chronic demyelination with axonal bulbar vacuolation. Our studies also revealed that CD40L (expressed on CD4+ T cells) upregulates upon MHV infection but is downregulated in CD4−/− mice CNS. This led to a further delineation of the CD4-microglia nexus at the molecular level using CD40L−/− mice. Results showed that the absence of CD40L renders mice highly susceptible to MHV infection due to reduced microglia/macrophage activation and significantly dampened effector CD4+ T recruitment to the CNS at the acute-adaptive bridging phase (day 7–10 p.i.) of inflammation. Moreover, CD40L−/− mice exhibited severe demyelination, axonal loss, and persistent poliomyelitis at the chronic phase of infection, highlighting the protective role of CD40-CD40L in MHV induced neuroinflammatory demyelination. Together, these studies highlight that migration of peripheral T cells and their interaction with microglia via CD40-CD40L is essential to eliminate the virus and provide long-term neuroprotection. These findings can lead to designing potential therapeutic interventions against MS, targeting CD40-CD40L interaction.