Neurotropism of Rabies Virus

The relative susceptibility of neurons and glia, grown as monolayers in vitro , to rabies virus infection was explored. Established cell lines of neuronal or glial phenotype and primary cultures of cells derived from mouse dorsal root ganglia (DRG) or brain were used as homologues of the targets of rabies virus in the nervous system. Fixed rabies virus (CVS) strain was used in most experiments; other fixed rabies strains (PV, HEP, ERA) and a street rabies virus isolate were used in some. Virus-cell tropism was determined by immunofluorescence assay for rabies nucleocapsid antigen and cell permissivity was assessed by titration of virus yields. Neuronal cells always exhibited a much greater susceptibility to infection and a greater propensity to sustain viral growth. By immunofluorescence, 90–100% of neurons commonly had viral inclusion bodies, while doses of the virus three to four orders of magnitude higher still left >99% of astrocytes, in brain cell cultures and 90 ± 5% of the non-neuronal cells in DRG cultures without any obvious signs of rabies virus. Neuroblastoma cells (95 ± 5% with viral antigens) produced viral yields about four orders of magnitude higher than glioma cells (10 ± 5% with viral antigens). Though the overall infectivity of street virus was lower than that of fixed virus strains, a significantly higher viral tropism for neurons than for glia was maintained. Thus, primary neuronal cultures offer a means of exploring molecular events in rabies virus infection and their role in pathogenesis.