BLV-infected lymphocytes exhibit two patterns of expression as determined by Ig and CD5 markers.

Lymphocytes were defined by their cell surface markers, Ig and CD5 in three groups of cows naturally infected with bovine leucosis virus (BLV). Lymphocytes were enumerated and groups were designated BLV seropositive with persistent lymphocytosis (BLV + PL +), BLV seropositive without persistent lymphocytosis (BLV + PL-) and BLV negative. The competence of peripheral blood mononuclear cells (PBMC) from the tested cows to express these two markers was determined by the double staining immunofluorescence procedure. Cows which developed persistent lymphocytosis (PL) as a result of BLV infection consequently underwent massive proliferation of B lymphocytes which express both Ig and CD5 antigens. In contrast, cows which were defined as BLV positive and PL negative showed a remarkable decrease of CD5 + Ig-, CD5- Ig+ and CD5+ Ig+ cells and also in the total number of lymphocytes. We suggest that BLV infection affects bovine lymphocytes through two different pathways of expression which might be related to the genetic properties of the target cells.