Further phenotypic characterization of target cells for bovine leukemia virus experimental infection in sheep.

To determine the phenotype of target cells for bovine leukemia virus (BLV) infection in sheep, we analyzed blood lymphocytes from BLV-infected clinically healthy and leukemic sheep by use of monoclonal antibodies. In clinically healthy and leukemic sheep that were BLV-infected, the blood concentration of T lymphocytes was within normal values, but the number of B lymphocytes was increased in several cases. In addition, the number of blood lymphocytes expressing the BLV antigen correlated well with that of B lymphocytes. Double immunofluorescence staining demonstrated that lymphocytes expressing BLV antigens bore B-cell but not T-cell surface markers. Moreover, neoplastic cells in the lymph nodes of leukemic sheep were stained immunohistochemically with an anti-B monoclonal antibody but not with any of anti-T monoclonal antibody tested, indicating that tumor cells are of B-lymphocyte origin. Collectively, these results show that BLV antigen-positive cells obtained from BLV-infected sheep that have no clinical signs and BLV-induced lymphosarcoma cells belong to the B-lymphocyte lineage.