Flow Cytometric Determination of the Expression of gp 51 Protein of Bovine Leukaemia Virus in Experimentally Infected Sheep

The study was performed on lambs experimentally infected with bovine leukaemia virus (BLV). The presence of BLV antibodies in sera of infected animals was detected by agar gel immunodiffusion test and ELISA. Proviral DNA was detected by PCR and nested PCR. Dual-colour flow cytometry analysis was performed with the use of specific monoclonal antibodies against lymphocyte CD markers and gp51 viral envelope protein, followed by incubation with fluorescent-labelled secondary antibodies conjugated with FITC or PE. Gp51 viral envelope protein was detected in tumours caused by BLV infection. The BLV infection resulted in depletion of CD4+ lymphocytes, increase in CD8+ lymphocytes, and decrease in CD4+ to CD8+ ratio in infected sheep. Proliferation of IgM+ CD19+ cells was also detected. These cells had an immature character without tendency to differentiate, and their vitality was prolonged. Flow cytometry enabled detection of gp51 expression in sheep blood lymphocytes at the early stages of the infection, before detection of serum antibodies using ELISA.