Effect of Cadmium and Lead on [h]-thymidine Uptake in Sheep Lymphocytes Infected with Bovine Leukaemia Virus

Effect of cadmium (Cd II) and lead (Pb II) was determined on cell proliferation, DNA synthesis, DNA repair, and DNA polymerase activity. The experiments were done on lymphocytes obtained from sheep infected with bovine leukaemia virus (BLV) and non-infected animals. All methods were based on [ H]-thymidine incorporation into DNA and performed in cell cultures stimulated by mitogens. Lymphocytes exposed to cadmium resulted in suppression of proliferation and DNA repair in both BLV infected and non-infected cells, but DNA polymerases showed lower activity only at higher concentration of cadmium. Lymphocytes treated with lead showed increased proliferation of non-infected cells, but significantly suppressed the proliferation of BLV infected cells. Activity of the DNA polymerases decreased proportionally to lead concentration in all BLV-infected lymphocyte cultures. The results suggest that the metals may affect the lymphocyte directly by altering the synthesis of cellular DNA and thereby influence the immune responses. In conclusion, it can be assumpted that exposure of lymphocytes to cadmium or lead in the presence of BLV infection can decreased their ability to mount immune response against viral pathogens.