Evidence that the paramyxovirus simian virus 5 can establish quiescent infections by remaining inactive in cytoplasmic inclusion bodies

Abstract

Following infection of BALB/c fibroblastic (BF) cells with simian virus 5 (SV5) only low levels of infectious virus were produced and the majority of cells survived the infection. However at 1 day post-infection (p.i.), near normal levels of all the virus proteins were synthesized and the virus genome was replicated. RNA analysis of the infected cells revealed that the levels of viral genomic RNA remained high over 5 days of infection, but that viral mRNA levels were significantly reduced by 3 days p.i, There was no evidence for the accumulation of defective genomes over this period. The reduction in mRNA levels was reflected by a concomitant decrease in the rate of ongoing viral protein synthesis. Despite the apparent decrease in viral transcription, comparative measurements of the relative levels of the different virus proteins at various times p.i. revealed that the levels of the P and NP proteins were similar at 1 and 5 days p.i. but the levels of V, M and F declined. Immunofluorescence analysis supported this data showing that at later times p.i., although there were some cells which were positive for all the viral proteins, a high proportion of cells were strongly positive for NP and P but negative for M, F and HN proteins. In these cells, NP and P were often located in discrete cytoplasmic foci. A series of cell lines were established from BF cells that had been infected at high multiplicity. Immunofluorescence studies showed that only a minority of cells in these cell lines were infected. This suggests that upon cell division, in a proportion of cells, virus replication was not taking place; otherwise it would be expected that all the daughter cells would remain infected. However, upon co-cultivation of these cells with Vero cells (cells that are fully permissive for SV5 replication), non-defective virus could be recovered. Virus cytoplasmic inclusion bodies could still be detected in a small proportion of BF cells that had been infected at high m.o.i, and passaged 10 times over a 12 week period, and again low levels of infectious virus could be recovered from these cells. It is proposed that in these persistently infected cells, the majority of virus genomes reside in an inactive form in cytoplasmic inclusion bodies but from which virus may occasionally be reactivated. Studies on cell clones obtained from a Vero cell line persistently infected with SV5 for over 100 passages (in which there are large numbers of defective genomes) also showed that not all daughter cells remained infected upon cell division. At later times p.i. in BF cells, when the majority of cells were positive for only NP and P, the cells became more resistant to cell-mediated immune lysis. The significance of these results in terms of the biology and immunology of paramyxovirus infections is discussed.

STAT Protein Interference and Suppression of Cytokine Signal Transduction by Measles Virus V Protein

“…Similar granular structures are produced by paramyxovirus infections and, in some cases, by simple expression of the nucleocapsid protein along with the P, V, or C protein. These structures may be universal for the paramyxoviruses and have been observed for SV5 (12,45,46), type II human parainfluenza virus (36,61), respiratory syncytial virus (13), Sendai virus (44), and mumps virus (57). The exact function of these structures is still unknown, but it has been proposed previously that in murine fibroblasts which are persistently infected with SV5, these "cytoplasmic inclusion bodies" represent an inactive reservoir from which virus may occasionally be reactivated (12).…”

“…These structures may be universal for the paramyxoviruses and have been observed for SV5 (12,45,46), type II human parainfluenza virus (36,61), respiratory syncytial virus (13), Sendai virus (44), and mumps virus (57). The exact function of these structures is still unknown, but it has been proposed previously that in murine fibroblasts which are persistently infected with SV5, these "cytoplasmic inclusion bodies" represent an inactive reservoir from which virus may occasionally be reactivated (12). It has been more recently appreciated that STAT1 targeting by SV5 is defective in murine cell systems (10,39,66).…”

Interferon-Induced Alterations in the Pattern of Parainfluenza Virus 5 Transcription and Protein Synthesis and the Induction of Virus Inclusion Bodies

“…7). Indeed, cytoplasmic inclusion bodies may be a virus defense mechanism in which the virus can hide both from intracellular antiviral responses and adaptive immune responses (8,16). If this is the case, then it opens up the question as to whether the way in which viruses such as SV5 change their pattern of virus transcription and protein synthesis in response to the programmed IFN response may have been selected for during virus evolution.…”

Optimal Colocalization of TCR and CD8 as a Novel Mechanism for the Control of Functional Avidity

“…However, it should be noted that this correlation does not hold true in all cases. In addition, the levels of CD8 and LFA-1 have been shown to influence the amount of peptide/MHC required for activation (5)(6)(7)(8)(9).…”