Immune cells promote paralytic disease in mice infected with enterovirus D68

Enterovirus D68 (EV-D68) is associated with acute flaccid myelitis (AFM), a poliomyelitis-like illness causing paralysis in young children. However, mechanisms of paralysis are unclear, and antiviral therapies are lacking. To better understand EV-D68 disease, we inoculated newborn mice intracranially to assess viral tropism, virulence, and immune responses. Wild-type (WT) mice inoculated intracranially with a neurovirulent strain of EV-D68 showed infection of spinal cord neurons and developed paralysis. Spinal tissue from infected mice revealed increased levels of chemokines, inflammatory monocytes, macrophages, and T cells relative to controls, suggesting that immune cell infiltration influences pathogenesis. To define the contribution of cytokine-mediated immune cell recruitment to disease, we inoculated mice lacking CCR2, a receptor for several EV-D68-upregulated cytokines, or RAG1, which is required for lymphocyte maturation. WT, Ccr2 ^-/- , and Rag1 ^-/- mice had comparable viral titers in spinal tissue. However, Ccr2 ^-/- and Rag1 ^-/- mice had significantly less paralysis relative to WT mice. Consistent with impaired T cell recruitment to sites of infection in Ccr2 ^-/- and Rag1 ^-/- mice, antibody-mediated depletion of CD4 ⁺ or CD8 ⁺ T cells from WT mice diminished paralysis. These results indicate that immune cell recruitment to the spinal cord promotes EV-D68-associated paralysis and illuminate new targets for therapeutic intervention.