CD8⁺ T cells require perform to clear West Nile virus from infected neurons

Injury to neurons after West Nile virus (WNV) infection is believed to occur because of viral and host immune-mediated effects. Previously, we demonstrated that CB8⁺ T cells are required for the resolution of WNV infection in the central nervous system (CNS). CD8⁺ T cells can control infection by producing antiviral cytokines (e.g., gamma interferon or tumor necrosis factor alpha) or by triggering death of infected cells through perform- or Fas ligand-dependent pathways. Here, we directly evaluated the role of perforin in controlling infection of a lineage I New York isolate of WNV in mice. A genetic deficiency of perforin molecules resulted in higher viral burden in the CNS and increased mortality after WNV infection. In the few perforin-deficient mice that survived initial challenge, viral persistence was observed in the CNS for several weeks. CD8⁺ T cells required perforin to control WNV infection as adoptive transfer of WNV-primed wild-type but not perforin-deficient CD8⁺ T cells greatly reduced infection in the brain and spinal cord and enhanced survival of CD8-deficient mice. Analogous results were obtained when wild-type or perforin-deficient CD8⁺ T cells were added to congenic primary cortical neuron cultures. Taken together, our data suggest that despite the risk of immunopathogenesis, CD8⁺ T cells use a perforin-dependent mechanism to clear WNV from infected neurons.