Influence of Tegument Proteins of Pseudorabies Virus on Neuroinvasion and Transneuronal Spread in the Nervous System of Adult Mice after Intranasal Inoculation

摘要

Pseudorabies virus (PrV) is a neurotropic alphaherpesvirus that, after intranasal infection of adult mice, enters peripheral neurons and propagates to the central nervous system. In recent years we have analyzed the contribution of virus-encoded glycoproteins to neuroinvasion and transneuronal spread (reviewed in T. C. Mettenleiter, Virus Res. 92:197-206, 2003). We now extend our studies to analyze the role of tegument proteins in these processes. To this end, PrV mutants unable to express the UL11, UL37, UL46, UL47, and UL48 tegument proteins, as well as the corresponding rescued viruses, were intranasally instilled into 6- to 8-week-old CD1 strain mice. First, mean survival times were determined which showed that mice infected with the UL46 deletion mutant succumbed to the disease as early as wild-type PrV-infected animals. Survival times increased in the order: PrV-ΔUL47-, PrV-ΔUL11-, and PrV-ΔUL48-infected animals, a finding which parallels the growth phenotype of these viruses in cell culture. In contrast, none of the PrV-ΔUL37-infected animals died. Upon closer histological examination, all viruses except PrV-ΔUL37 were able to infect the nasal cavity and propagate to first- and second-order neurons as shown by two-color immunofluorescence. However, neuroinvasion was delayed in PrV-ΔUL47, PrV-ΔUL11, and PrV-ΔUL48, a finding that correlated with the extended survival times. Surprisingly, whereas PrV-ΔUL48 and PrV-ΔUL37 replicated to similar titers in cell culture which were ∼500-fold lower than those of wild-type virus, after intranasal infection of mice PrV-ΔUL48 was able to infect areas of the brain like wild-type PrV, although only after a considerably longer time period. In contrast, PrV-ΔUL37 was not able to enter neurons and was restricted to the infection of single cells in the nasal respiratory epithelium. Thus, our data demonstrate the importance of herpesviral tegument proteins in neuronal infection and show a different contribution of tegument proteins to the neuroinvasion phenotype of a neurotropic alphaherpesvirus.