Characterization of JHMV variants isolated from rat brain and cultured neural cells after wild type JHMV infection.

After intracerebral inoculation of wild type (wt) JHMV into 4 to 5 week-old Lewis rats, only variants with larger mRNA3 were selectively propagated and no wt JHMV was reisolated from the brain. Detailed analysis of a cloned virus from infected rat brain, c1-2, showed that the virus had larger mRNAs 2, 2a and 3 as compared with those of wt JHMV, while there was no such difference for other mRNAs. The E2 glycoprotein of a variant virus was also shown to be larger as compared with that of wt JHMV. Such selective replication of variants were also observed in neural cell culture after infection with wt JHMV. However, these variants isolated from the brain of infected rat (c1-2) and from infected neural cells (CNS virus) differed from each other in the amounts of mRNAs 2 and 2a as well as 65 K protein. All of these data suggest that the viruses with larger E2 glycoprotein have the growth advantage in rat brain cells, which could be responsible for acute encephalitis of rats after infection with wt JHMV.