The immune system response to viral infection of the CNS

In immunological terms the CNS is at a severe disadvantage in its ability to respond to infection by virus. First, both glial and neuronal cells normally do not express molecules of the major histocompatibility complex. Second, the most efficient cells for stimulating an immune response (leucocyte dendritic cells) are not present in the healthy CNS; and third, there is no specialized lymphatic drainage from the CNS to lymph nodes to enable the immune system to be quickly informed of the presence of an infection. Nevertheless, the immune system apparently copes with the vast majority of viral infections in the CNS. This is clearly evidenced by the reactivation of latent CNS viral infections in some immunosuppressed patients and the dramatic increase in the seventy of CNS disease in young or otherwise immunologically incompetent experimental animals infected with neurotropic viruses. The routes by which the CNS and the immune system may communicate and the varied ways in which an immune response may affect the outcome of a viral infection of the CNS are discussed.