Differences in the lymphoproliferative response of cattle and sheep to bovine leucosis virus infection.

Lymphoblastic leukaemia, preceded by a significantly increasing percentage of prolymphocytes in peripheral blood smears for from 12 to 68 weeks before death was a feature of sheep which developed lymphosarcoma following inoculation with the Australian strain of bovine leucosis virus (BLV). Lymphocytosis and/or the appearance of immature cells were a reliable predictor of tumour formation in sheep, but not in cattle. There was a terminal lymphoblastic leukaemia in only 43 of 84 cattle with lymphosarcoma. Differences in the morphological appearance and glycogen content of the leukaemic lymphoblasts of sheep and cattle were observed. In spite of these differences the high frequency of lymphocytosis and lymphosarcoma in experimentally infected sheep suggests that they could be a useful model for studying the pathological and immunological responses to BLV infection.