The correlation between the direct and indirect detection of bovine leukemia virus infection in cattle

Ninety-three cattle from a herd naturally infected with bovine leukemia virus (BLV) were tested for the presence of BLV infection by two indirect indicators, anti-BLV antibodies and lymphocytosis, and two direct indicators, BLV provirus and BLV gp51 antigen expression in peripheral blood mononuclear cells (PBMC). Forty-eight percent (45/93) of the cattle were seropositive, and of these, 53% (24/45) were provirus-positive. Freshly isolated PBMC were negative for gp51 antigen expression, but 11 cattle were positive following short-term culture of their PBMC; 10 of these were seropositive/provirus-positive cattle, and one was a seropositive/provirus-negative cow. Lymphocytosis was present in eight cattle, all of which were seropositive/provirus-positive/gp51-positive. Four cattle were provirus-positive, but negative for all other indicators of BLV infection; a second blood sample was collected from three of these cattle at a later date, at which time two of the three had seroconverted. These results suggest that depending on the stage of the infection, the pathogenesis of BLV in cattle may involve fundamental differences in the host-viral relationship, including the number of cells infected or the number of copies of integrated provirus per cell, regulation of expression of viral antigens, induction of the anti-viral immune response, and the polyclonal or monoclonal proliferation of lymphocytes.