Lactate dehydrogenase-elevating virus entry into the central nervous system and replication in anterior horn neurons

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The initial replication of lactate dehydrogenase-elevating virus (LDV) in mice, its invasion of the central nervous system (CNS) and infection of anterior horn neurons in C58 and AKXD-16 mice were investigated by Northern and in situ hybridization analyses. Upon intraperitoneal injection, LDV replication in cells in the peritoneum was maximal at 8 h post-infection (p.i.). Next, LDV infection was detected in bone marrow cells and then in macrophage-rich regions of all tissues investigated (12 to 24 h p.i.). By 2 to 3 days p.i., LDV RNA-containing cells had largely disappeared from all non-neuronal tissues due to the cytocidal nature of the LDV infection of macrophages. In the CNS at 24 h p.i. LDV replication was very limited and confined to cells in the leptomeninges. LDV replication in the cells of the leptomeninges should result in the release of progeny LDV into the cerebrospinal fluid and thus its dissemination throughout the CNS. However, in C58 and AKXD-16 mice, which are susceptible to paralytic LDV infection, only little LDV RNA and few LDV-infected cells were detectable in the spinal cord until at least 10 days p.i. Extensive cytocidal infection of anterior horn neurons occurred only shortly before the development of paralytic symptoms between 2 and 3 weeks p.i. The reason for the relatively long delay in LDV infection of anterior horn neurons is not known. No LDV RNA or LDV RNA-containing cells were detected in the brain, except in the leptomeninges at early times after infection.