Epidemiological and pathological studies of a familial thymic lymphosarcoma in bovine species.

A total of 216 cases of the thymic form of bovine leukosis were observed in Holstein calves in several departments of France over a period of 18 months. Almost all of these calves were sired by the same bull. The calves were negative for bovine leukemia virus-specific antibodies. Morphological studies, including light and electron microscopic cytology, and immunophenotyping were performed in 38 cases. The tumor cells exhibit membrane markers (T-cell antigens) at variable levels, which indicate that they are T-lymphoid derived. The cells are maintained at a very early stage of differentiation as indicated by TdT enzyme activity and the presence of MHC class II antigen.