Flow cytometry determination of Bcl-2 expression in animals infected with bovine leukaemia virus

Investigations were performed in lambs experimentally infected with blood lymphocytes of leukaemic cow. The presence of specific bovine leukaemia virus (BLV) antibodies in sera of infected animals was detected in agar gel immunodiffusion test and ELISA. Proviral DNA was detected with PCR and nested PCR. Dual-colour flow cytometry analysis with the use of specific monoclonal antibodies (for lymphocyte CD markers, proliferating cell nuclear antigen (PCNA) and Bcl-2 protein) and conjugates labelled with FITC or PE was performed. The results demonstrated much higher level of PCNA in leukaemic lymphocytes than in healthy ones and these values were dependent on the stage of the disease. Expression of Bcl-2 protein was much stronger in lymphocytes of infected animals than in control group. The BLV infection caused depletion of CD4 lymphocytes in infected sheep and proliferation of IgM+ CD19+ cells. These cells had immature character without tendency to differentiation, and their vitality was prolonged due to Bcl-2 protein, which physiologically blocks apoptosis.