Borna disease virus (BDV) replicates only in cells in thelsquo; central (CNS) and peripheral (PNS) nervous system in adult rats. Infection of the nervous system is associated with a transient, intense mononuclear meningoencephalitis and immune-mediated loss of BDV-infected neurons. The identification of BDV antigen in neurons and the accompanying immunologically-specific lysis of these cells led to the prediction that the CNS would be virus-free after the animal had recovered from encephalitis. However, BDV infectivity and antigen persist for the lifetime of the animal. It appeared, therefore, that other neural cells might be hosts for viral replication and provide a reservoir for the virus. Morphological criteria were used to identify astrocytes and Schwann cells which expressed BDV antigensin vivo. Borna disease virus (BDV) infected astrocytes were identified by double labeling tissue sections with combined cell-specific and BDV-spccific antibodies in an avidin-biotin immunocy-tochemical assay. Examination of serial 1 micrometer-thick cryosections of hippocampus and sciatic nerve preparations revealed several cells that expressed both glial and BDV antigens. Infectious virus was recovered from cultures of Schwann cells from infected rats. Borna disease virus-infected glial elements persisted beyond the period of inflammation and massive neuronal destruction, and represented a major class of infected cells during chronic disease.
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