Mouse hepatitis virus (MHV-2). Plaque assay and propagation in mouse cell line DBT cells.

Various factor sinfluencing the plaque formation of mouse hepatitis virus (MHV-2) in DBT cell monolayers were studied and a practical method for plaque assay was developed. Infected DBT cells yielded high-titered virus and were a satisfactory source of complement-fixing viral antigen. The predominant cytopathic effect of MHV-2 in DBT cells was cell rounding and detachment, but no syncytial formation was observed. Fluorescent antibody staining revealed specific fluorescence only in the cytoplasm of infected DBT cells. In one-step growth experiment, newly formed virus was first recognized within 4-hr postinfection and showed subsequently a rapid exponential increase. Release of newly formed virus from the cell was rapid, and a continuous release lasted for a certain period of time. The average per-cell yield of active virus was estimated to be about 6-7 X 10(2) plaque-forming units.     

Properties of influenza C virus grown in cell culture.

Influenza C virus was propagated successfully in primary chicken embryo lung (CEL) and fibroblast cells and in Madin-Darby canine kidney (MDCK) cells. In other cell lines, either no virus or only noninfectious hemagglutinin (HA) was produced. In productively infected cells (CEL), HA and infectious virus appeared by 24 h and reached a maximum by 36 to 48 h, cell-associated virus remaining at a constant low level. Infected Vero cells produced noninfective HA by 24 h which also remained predominantly cell associated until 60 to 72 h, when the cells disintegrated. Viral antigen was demonstrable on membranes of both CEL- and Vero-infected cells at 24 h; Vero cells yielded membrane vesicles containing HA, but none of the spherical or filamentous viral particles synthesized in CEL cells. Influenza C virus produced in cell culture or in eggs differed in several important respects from A and B viruses and from Newcastle diseases virus. All influenza C preparations, regardless of infectivity or source, lacked detectable neuraminidase activity, yet retained the ability specifically to inactivate receptors only for influenza C. Influenza C HA was not inhibited by soluble glycoproteins highly active against HA of A virus. A rat serum glycoprotein uniquely inhibited influenza C by binding to the surface components of virious.     

The role of circulating interferon in the modifications of immune responsiveness by mouse hepatitis virus (MHV-3).

MHV-3 modifies the humoral immune response to SRBC. During acute infections timing was critical: infecting mice before antigen administration led to immunodepression. Simultaneous injection with virus and SRBC resulted in immunostimulation. Persistent MHV-3 infections were associated with a chronic immunodepression. The presence of circulating interferon (IF) was well correlated with these modifications. IF peaking before antigen was associated with immunodepression whereas IF secretion after antigen was associated with immunostimulation. Low, permanent levels of IF were associated with chronic immunodepression. Since IF is, up to now, the only product of activated lymphocytes that has been shown to modulate immune responses, our results suggest that induction of IF by MHV-3 may be the main mechanism by which this virus modifies immune responsiveness. Moreover, we have shown that MHV-3 infection in susceptible mice diminishes the secretion of lymphocyte IF in response to Sendai virus. In these animals, the thymus cortex was profoundly depleted although the thymus medulla remained unchanged. The MHV-3 infection may, therefore, interfere with a subpopulation of IF-secreting lymphocytes. The possible physiologic role of such lymphocyte subpopulation in terms of host-virus relationships is discussed.     

Mouse Hepatitis Virus (MHV-2)

Various factor sinfluencing the plaque formation of mouse hepatitis virus (MHV-2) in DBT cell monolayers were studied and a practical method for plaque assay was developed. Infected DBT cells yielded high-titered virus and were a satisfactory source of complement-fixing viral antigen. The predominant cytopathic effect of MHV-2 in DBT cells was cell rounding and detachment, but no syncytial formation was observed. Fluorescent antibody staining revealed specific fluorescence only in the cytoplasm of infected DBT cells. In one-step growth experiment, newly formed virus was first recognized within 4-hr postinfection and showed subsequently a rapid exponential increase. Release of newly formed virus from the cell was rapid, and a continuous release lasted for a certain period of time. The average per-cell yield of active virus was estimated to be about 6–7 × 10² plaque-forming units.     

戊型肝炎病毒细胞培养模型的研究进展

戊型肝炎病毒（ HEV）体外细胞培养模型的建立有助于阐明HEV的感染、复制及其致病机理,有利于新型抗病毒药物和疫苗的研发与评估。近年来国内外对HEV细胞培养模型的报道很多,但所用细胞系、感染方法及病毒的复制效果等不尽相同。因此,对近年来HEV细胞培养模型的研究进展进行了综述。     

Effect of methadone administration on MHV-3 virus-induced experimental hepatitis in the mouse

Mice treated with 15 mg/Kg/day methadone and infected with MHV-3 virus after 7 days did not show increased susceptibility to MHV-3 virus infection, did not develop more serious forms of hepatitis and not mortality did not increase with respect to the controls. Drug administration was continued for the duration of the experiment.     

RNA of mouse hepatitis virus.

The RNA of mouse hepatitis virus, a coronavirus, was isolated from the virus released early in the infection and analyzed by sucrose gradient sedimentation and electrophoresis. It was found to consist of a piece of single-stranded RNA of about 60S. Its molecular weight was estimated to be 5.4 X 10(6) by electrophoresis in methylmercury-agarose gels. At least one third of the RNA contained polyadenylated sequences. It is, therefore, probably positive stranded. The virus harvested late in the infection contained, in addition to 60S, some 30 to 50S RNA that are possibly degradation products of the 60S RNA. No difference in the electrophoretic behavior could be detected between the RNA isolated from a pathogenic (JHM) and a nonpathogenic (A59) strain.     

Production of infectious hepatitis C virus in cell culture

Hepatitis C virus (HCV) is a major public health problem, infecting an estimated 170 million people worldwide. Current therapy for HCV-related chronic hepatitis is based on the use of interferon. However, virus clearance rates are insufficient. Investigations to develop the anti-viral therapy or to understand the life cycle of this virus have been hampered by the lack of viral culture systems. We isolated the JFH-1 strain from a patient with fulminant hepatitis, and the JFH-1 subgenomic replicon could replicate efficiently in culture cell without adaptive mutation. Recently, we developed the HCV infection system in culture cells with this JFH-1 strain. The full-length JFH-1 RNA was transfected into Huh7 cells. Subsequently, viral RNA efficiently replicated in transfected cells and viral particles were secreted. Furthermore, secreted virus displayed infectivity for naive Huh7 cells. This system provides a powerful tool for studying the viral life cycle and constructing anti-viral strategies.