Cytolytic activity induced by intramuscular injection of plasmid DNA expressing the nucleocapsid protein of the JHM strain of mouse hepatitis virus into C57BL/6 mice.

We constructed plasmids expressing mRNA7 coding the nucleocapsid (N) protein of JHM strain of MHV (JHMV) under the control of Rous sarcoma virus (RSV) LTR or human elongation factor (EF) 1a promoter, referred to as pRSV-mRNA7 and pEF-mRNA7, respectively. Although only a slight level of cytolysis was observed by the spleen cells from C57BL/6 mice injected intramuscularly with pEF-mRNA7, the spleen cells from the mice administered with pRSV-mRNA7 showed a significant level of cytolytic activities against the cells expressing the viral N protein. The difference in the level of specific cytolysis might have been mainly due to a difference in the expression levels of the N protein in the muscles between the mice injected with pEF-mRNA7 and pRSV-mRNA7, since the specific activity of chloramphenicol acetyltransferase (CAT) in muscles from the mice injected with plasmid DNA expressing CAT gene directed by RSV LTR was significantly higher than that in those administered by the plasmid DNA directed by EF-1a promoter.