EXPRESSION OF HEMAGGLUTININ ESTERASE BY A MOUSE HEPATITIS-VIRUS CORONAVIRUS DEFECTIVE-INTERFERING RNA ALTERS VIRAL PATHOGENESIS/

A defective-interfering (DI) RNA of mouse hepatitis virus (MHV) was de veloped as a vector for expressing MHV hemagglutinin/esterase (HE) pro tein. The virus containing an expressed HE protein (A59-DE-HE) was gen erated by infecting cells with MHV-A59, which does not express HE, and transfecting the in vitro-transcribed DI RNA containing the HE gene. A similar virus (A59-DE-CAT) expressing the chloramphenicol acetyltran sferase (CAT) was used as a control. These vi ruses were inoculated in tra cerebrally into mice, and the role or the HE protein in viral path ogenesis was evaluated. Results showed that all mice infected with par ental A59 or A59-DE-CAT succumbed to infection by 9 days postinfection (p.i.), demonstrating that inclusion of the DI did not by itself alte r pathogenesis. In contrast, 60% of mice infected with A59-DE-HE survi ved infection. HE-or CAT-specific subgenomic mRNAs were detected in th e brains at days 1 and 2 p.i. but not later, indicating that the genes in the DI vector were expressed only in the early stage of viral infe ction. No significant difference in virus titer or viral antigen expre ssion in brains was observed between A59-DE-HE-and A59-DE-CAT-infected mice. suggesting that virus replication in brain was not affected by the expression of HE. However, at day 3 p.i. there was a slight increa se in the extent of inflammatory cell infiltration in the brains of th e A59-DE-HE-infected mice. Surprisingly, virus titers in the livers of A59-DE-HE-infected mice were 3 log(10) lower than that of the A59-DE- CAT-infected mice at day 6 p.i. Also, substantially less necrosis and viral antigen were detected in the livers of the A59-DE-HE-infected mi ce. This may account for the reduced mortality of these mice. The poss ible contribution of the host immune system to this difference in path ogenesis was analyzed by comparing the expression of four cytokines, R esults showed that both tumor necrosis factor-alpha and interleukin-6 mRNAs increased in the brains of the A59-DE-HE-infected mice at day 2 p.i., whereas interferon-gamma and interleukin-1 alpha mRNAs were simi lar between A59-DE-HE-and A59-DE-CAT-infected mice. These data suggest that the transient expression of HE protein enhances an early innate immune response, possibly contributing to the eventual clearance of vi rus from the liver. This study indicates the feasibility of the DI exp ression system for studying roles of viral proteins during MHV infecti on. (C) 1998 Academic Press.