IMR Press / FBL / Volume 12 / Issue 4 / DOI: 10.2741/2165

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on as a courtesy and upon agreement with Frontiers in Bioscience.

Cell dynamics and immune response to BLV infection: a unifying model
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1 Molecular and Cellular biology, FNRS-FUSAG, Gembloux, Belgium
2 Department of Immunology, Imperial College, London, UK
3 GlaxoSmithKline Biologicals, Rixensart, Belgium
4 Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Canada
5 U892 INRA, Jouy-en-Josas, France
6 Department of Virology, Veterinary and Agrochemical Research Centre, Uccle, Belgium
7 Zootechny unit, FUSAG, Gembloux, Belgium
8 Department of Immunology, University of Toronto, Toronto, Canada
9 Unité d'oncogenèse virale, CNRS UMR5537 Centre Leon Bérard, Lyon, France
10 Veterinary Research Institute, Pulawy, Poland
Academic Editor:Heribert Stoiber
Front. Biosci. (Landmark Ed) 2007, 12(4), 1520–1531;
Published: 1 January 2007
(This article belongs to the Special Issue Immune responses to retroviral infections)

Bovine Leukemia virus (BLV) is the natural etiological agent of a lymphoproliferative disease in cattle. BLV can also be transmitted experimentally to a related ruminant species, sheep, in which the pathogenesis is more acute. Although both susceptible species develop a strong anti-viral immune response, the virus persists indefinitely throughout life, apparently at a transcriptionally silent stage, at least in a proportion of infected cells. Soon after infection, these humoral and cytotoxic activities very efficiently abolish the viral replicative cycle, permitting only mitotic expansion of provirus-carrying cells. Short term cultures of these infected cells initially indicated that viral expression protects against spontaneous apoptosis, suggesting that leukemia is a process of accumulation of long-lived cells. This conclusion was recently reconsidered following in vivo dynamic studies based on perfusions of nucleoside (bromodeoxyuridine) or fluorescent protein markers (CFSE). In sheep, the turnover rate of infected cells is increased, suggesting that a permanent clearance process is exerted by the immune system. Lymphocyte trafficking from and to the secondary lymphoid organs is a key component in the maintenance of cell homeostasis. The net outcome of the immune selective pressure is that only cells in which the virus is transcriptionally silenced survive and accumulate, ultimately leading to lymphocytosis. Activation of viral and/or cellular expression in this silent reservoir with deacetylase inhibitors causes the collapse of the proviral loads. In other words, modulation of viral expression appears to be curative in lymphocytic sheep, an approach that might also be efficient in patients infected with the related Human T-lymphotropic virus type 1. In summary, a dynamic interplay between BLV and the host immune response modulates a complex equilibrium between (i) viral expression driving (or) favoring proliferation and (ii) viral silencing preventing apoptosis. As conclusion, we propose a hypothetical model unifying all these mechanisms.

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