Detection of proviral DNA of bovine leukaemia virus in cattle by a combination of in-situ hybridization and the polymerase chain reaction

Bovine leukaemia virus (BLV) proviral DNA was detected in lymphocytes isolated from cattle with persistent lymphocytosis (PL) by the polymerase chain reaction (PCR) and in-situ hybridization (ISH) with a biotinylated pX DNA probe. Many positive cells were observed when short-term culture and a combination of ISH with PCR were used. Immunohistochemical examination of lymphocytes isolated from the lymph node showed that BLV attached mainly to surface immunoglobulins (SIg) of positive B lymphocytes, and to a few tumour-associated antigen (TAA)-, PanT-, and CD8-positive cells and non-CD4 positive cells. Electron microscopical examination revealed colloidal gold particles within the nuclei and cytoplasm of lymphocytes. Lymphoid cells from neoplastic lymph node of enzootic bovine leukosis (EBL) cases gave particularly strong positive signals with the ISH-PCR method. The technique of combined ISH and PCR with a biotinylated pX probe may prove useful in future studies of EBL.