IN-VIVO LEUKOCYTE TROPISM OF BOVINE LEUKEMIA-VIRUS IN SHEEP AND CATTLE

Bovine leukemia virus (BLV), an oncovirus related to human T-cell leuk emia virus type I, causes a B-cell lymphoproliferative syndrome in cat tle, leading to an inversion of the T-cell/B-cell ratio and, more rare ly, to a B-cell lymphosarcoma. Sheep are highly sensitive to BLV exper imental infection and develop B-cell pathologies similar to those in c attle in 90% of the cases. BLV tropism for B cells has been well docum ented, but the infection of other cell populations may also be involve d in the BLV-induced lymphoproliferative syndrome, We thus looked for BLV provirus in other leukocyte populations in sheep and cattle by usi ng PCR. We found that while B cells harbor the highest proviral load, CD8(+) T cells, monocytes, and granulocytes, but not CD4(+) T cells, a lso bear BLV provirus. As previously described, we found that persiste nt lymphocytosis in cows is characterized by an expansion of the CD5() B-cell subpopulation but we did not confirm this observation in shee p in which the expanded B-cell population expressed the CD11b marker. Nevertheless, BLV could be detected both in bovine CD5(+) and CD5(-) B cells and in sheep CD11b(+) and CD11B(-) B cells, indicating that the restricted BLV tropism for a specific B-cell subpopulation cannot exp lain its expansion encountered in BLV infection. Altogether, this work shows that BLV tropism in leukocytes is wider than previously thought . These results lead the way to further studies of cellular interactio ns among B cells and other leukocytes that may intervene in the develo pment of the lymphoproliferative syndrome induced by BLV infection.