Interfering virus

Abstract: Publisher Summary This chapter presents in molecular terms the explanation for immunologic events accompanying lymphocytic choriomeningitis (LCM) infection, including the dual recognition of viral and histocompatibility antigens essential for T cell action and the modulation of viral expression result from the immune response. It discusses the important aspects of nonimmunologic regulation of viral infection particularly the role of defective interfering virus. Lymphocytic choriomeningitis virus (LCMV) and the infection it causes are important subjects of biomedical investigation. First, this virus sporadically causes human illness. The study of LCMV and the disease it causes in its natural murine host has provided the initial findings to open new fields in viral immunobiology, viral immunopathology, and cell–cell recognition. The apparent increased virulence of LCMV on passage through hamsters and the fact that LCMV infection can be transmitted from hamsters to humans suggest important concerns not only for investigators working with LCMV but for experimentalists who use hamsters or hamster tissues in their studies.

Abstract: Publisher Summary This chapter describes the experimental conditions required for the production of fully active and incomplete influenza virus. Well-adapted laboratory strains of fully active virus are grown from dilute seeds and harvested when the virus activity becomes maximal. The formation of large amounts of incomplete influenza virus has been observed in embryonated eggs and in a number of other host-cell systems. Incomplete influenza virus is produced also in tissue cultures seeded with large concentrations of Standard virus. Incomplete virus particles are practically undistinguishable from the fully active virus in size, shape, and biologic surface characteristics. They differ from the fully active particles by having a lower sedimentation constant, by the apparent lack of infectivity, and by their capacity to interfere with and inhibit the propagation of the infective virus. The chapter also discusses the various hypotheses about the mechanism responsible for the formation of incomplete virus, along with the nature and origin of the virus.

Abstract: Defective interfering virus (DI) particles represent a major controlling element of virus replication. They are constantly generated at low levels by infectious virus and only amplify to interfering levels when the parent helper vims is abundant. This autointerference phenomenon, as it was called when first discovered, is achieved by rearrangements and deletions of the standard virus genome such that the resulting “incomplete form” of the virus can preferentially replicate.

Abstract: We have recovered infectious Sendai virus (SeV) from full-length cDNA (FL-3) by transfecting this cDNA and pGEM plasmids expressing the nucleocapsid protein (NP), phosphoprotein and large proteins into cells infected with a vaccinia virus which expresses T7 RNA polymerase. These cells were then injected into chicken eggs, in which SeV grows to very high titers. FL-3 was marked with a BglII site in the leader region and an NsiI site (ATGCAT) in the 5' nontranslated region of the NP gene, creating a new, out-of-frame, 5' proximal AUG. All the virus stocks generated eventually removed this impediment to NP expression, by either point mutation or recombination between FL-3 and pGEM-NP. The recovery system was found to be highly recombinogenic. Even in the absence of selective pressure, one in 20 of the recombinant SeV generated had exchanged the NP gene of FL-3 with that of pGEM-NP. When a fifth plasmid containing a new genomic 3' end without the presumably deleterious BglII site was included as another target for recombination, the new genomic 3' end was found in the recombinant SeV in 12 out of 12 recoveries. Using this approach, a novel copy-back nondefective virus was generated which interferes with wild-type virus replication.