Time course changes in peripheral B-cell clonality in a Japanese Black bull with enzootic bovine leukosis.

A 38-month-old Japanese Black bull presenting with anorexia was given supportive treatment without improvement. Findings including bovine leukemia virus positivity and monoclonal B-cell proliferation strongly suggested the onset of enzootic bovine leukosis (EBL). Pathological findings confirmed the diagnosis of EBL. B-cell clonality were analyzed over time using pre-onset preserved genomic DNA at ages 6 months, 16 months, and 30 months. In the B-cell clonality analysis, two minor peaks at 140 and 220 bp were observed before onset, but another large peak at 175 bp appeared at the time of EBL diagnosis. Although the reason for the proliferation of an independent clone is unknown, detection of clonality abnormalities may lead to the detection of cattle at high risk of developing EBL.