Analysis of the Distribution of Neuropathogenic Retroviral Antigens Following PVC211 or A8‐V Infection

A8-V and PVC211 are neuropathogenic strains of the Friend murine leukemia virus (Fr-MLV) that cause spongiosis in the rat brain after infection at birth. PVC211 exhibited stronger neuropathogenicity than A8-V, and induced more severe neurological symptoms such as hind-leg paralysis. These symptoms correlated with the neuropathological spread and intensity, which were more severe in the spinal cord of rats infected with PVC211 than in those infected with A8-V, without exhibiting neuropathological differences in other areas of the CNS. Interestingly, virus titers recovered from infected spinal cords were similar in PVC211 and A8-V infected animals. However, in the spinal cord infected with PVC211, glial cells attained higher immunohistochemical expression scores for the viral surface antigen, gp70 (Env) than in the A8-V infected spinal cord, although expression levels of viral antigens in blood vessel walls were similar in A8-V and PVC211 infections. Furthermore, many of those glial cells which carried viral antigens were found, by double immunostaining, to be microglia. The results suggested that the spread of viral antigen positive microglia plays an important role in forming the different neuro-pathogenicity observed in A8-V and PVC211 infections.