No abstract

An abattoir survey for bovine enzootic leukosis revealed that severe splenomegaly and hepatomegaly were observed in a heifer (case 1) and a steer (case 2), respectively, in addition to great enlargement of certain lymph nodes. Both cases tested positive for bovine leukemia virus (BLV) by polymerase chain reaction. Histologically, the neoplastic tissues in case 1 were characterized by a mantle zone growth pattern of medium-sized cells showing a transition to highly pleomorphic and atypical cells. Similar histological characteristics were also observed in case 2, but neoplastic mantle cells forming focal lesions were more pleomorphic than in case 1. B cell markers CD20 and CD79a were expressed in cases 1 and 2, as well as CD5 and cyclin D1, which are important markers for human mantle cell lymphoma. Cases of pleomorphic B cell lymphoma with large abdominal tumor masses are thought to be derived from body cavity B-1 cells, whereas this study suggests that nodal pleomorphic B cell lymphoma is of mantle cell origin.

Pleomorphic B cell lymphoma was detected in a small number of lymph nodes in an 8-year-old Holstein cow with persistent lymphocytosis associated with bovine leukemia virus (BLV). Necropsy showed enlargement of the left superficial inguinal and right deep inguinal lymph nodes. Large numbers of BLV copies were detected by real-time polymerase chain reaction analysis in the enlarged nodes, whereas little BLV was found in normal-sized lymph nodes. Histologically, the enlarged lymph nodes were occupied by diffusely growing pleomorphic cells. In a few other lymph nodes, in contrast, extensive areas of neoplastic mantle cells showing a transition to more malignant pleomorphic cells were observed. These virological and histological findings indicate that large numbers of viral copies may be closely related to transformation from neoplastic mantle cells to pleomorphic lymphoma cells. The current study supports the view that nodal pleomorphic B cell lymphoma is of mantle cell origin.

We examined a 26-month-old steer with neoplastic lesions in the spleen, lymph nodes, heart and kidneys, characterized by pleomorphic lymphoid cells that were immunohistochemically positive for CD20. The presence of bovine leukemia virus (BLV) at >200,000 copies per 100,000 cells by quantitative RT-PCR was considered to be due to random integration of the provirus into the neoplastic cells´ genomes. Inverse PCR identified the presence of one, two, two and three different malignant clones in the heart, spleen, mesenteric node and blood, respectively. Because BLV can rapidly induce lymphoma and a high proviral load facilitates B-cell carcinogenesis, multiclonal tumor development was suspected in the present case.