Journal of General Virology, Vol 78, 153-162, Copyright © 1997 by Society for General Microbiology

ARTICLES

Bovine leukaemia virus-induced lymphocytosis in sheep is associated with reduction of spontaneous B cell apoptosis

I Schwartz-Cornil, N Chevallier, C Belloc, D Le Rhun, V Laine, M Berthelemy, A Mateo and D Levy
URA INRA d'Immuno Pathologie Cellulaire et Moleculaire, Maisons-Alfort, France. schwartz@jouy.inra.fr

Experimental inoculation of sheep with bovine leukaemia virus (BLV), a retrovirus homologous to the human T-lymphotropic virus type 1 (HTLV- 1), induces a chronic expansion of the B lymphocyte population (persistent lymphocytosis) and the development of a B cell leukaemia/lymphosarcoma syndrome. To gain insight into the mechanisms of BLV-induced lymphocytosis, we tested B cell survival capacity and cycling activity in peripheral blood mononuclear cells (PBMCs) from lymphocytotic, asymptomatic and control sheep. Interestingly, B cells from lymphocytotic sheep presented a lower level of spontaneous apoptosis (29%) in ex vivo cultures compared to that obtained with infected asymptomatic (42%) and control (57%/o) sheep PBMCs. Virus capsid (CA) synthesis was mainly found among surviving B cells and the percentage of CA-producing B cells correlated with the extent of B cell survival, indicating that BLV replication in B lymphocytes may promote protection from cell death. B cell survival was not linked with increases in expression of Bcl-2 mRNA or membrane leukosialin (CD43), although both are documented to be involved in some aspects of the B cell life-span. Finally, cell cycle analyses in freshly isolated PBMCs from lymphocytotic sheep revealed a slightly increased proportion of B cells in S phase compared to controls. Altogether, these data suggest that both BLV-induced B cell proliferation and extended survival are involved in the lymphocytotic stage encountered in BLV infection in sheep.

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