The immune response to infection can contribute to fatal disease, but is also necessary for recovery and virus clearance. Elimination of virus-infected cells from tissue requires elimination of all cells in which the virus is replicating. This can occur either by virus-induced or immune-mediated cytolysis. T cells are ideal for this purpose because they recognize viral antigen as processed antigen only in the context of cell surface-expressed MHC class I (CD8 + T cells) or of MHC class II (CD4 + T cells) and can possess cytotoxic properties. Neurons are long-lived essential cells that cannot be replaced, so a noncytolytic immune mechanism for virus clearance would be advantageous to the host to avoid death of surviving cells. If the immune clearance mechanism is damaging to the infected neuron, then the function of that neuron will be lost and the outcome for the host will be the same as if the virus infection had caused neuronal death.