Vet Pathol 31:103-105 (1994) BRIEF COMMUNICATIONS and CASE REPORTS The y6 T Cell Population in Sheep Experimentally Infected with Bovine Leukemia Virus

Bovine leukemia virus (BLV) is an exogenous retrovirus and associated with enzootic bovine leukosis (EBL)4 which often includes persistent lymphocytosis and development of B-cell lymphosarcoma/leukemia after a long latent period. Natural cases of malignant lymphomas are rare in sheep. Under experimental conditions, however, sheep are easily infected with BLV7 and develop B-cell lymphosarcoma/leu-kemia at a higher frequency and within a shorter period (1 to 3 years) than cattle. Sheep also show serologic and patho-logic responses to BLV similar to those in The lymphoid systems of sheep and cattle contain a large number of the CD4- CD8- “double-negative ” T lymphocyte s~bpopu la t ion~- ~ in striking contrast to the lymphoid systems of human and mouse. These double-negative lymphocytes are known to express the y6 chains of T cell receptor (TCR)2.