Functional evaluation of monocytes in cattle naturally infected with the bovine leucosis virus

Assuming that the bovine leukosis virus (BLV) alters quantitatively and qualitatively bovine circulating leukocyte subpopulations, thus influencing the innate immune response, monocytes function in BLV-infected cattle was assessed. Peripheral blood was obtained from 10 BLV-negative cows (SN), 10 naturally BLV-infected, non-lymphocytotic cows (AL), and 10 BLV-infected cows with persistent lymphocytosis (PL). Monocytes were isolated by density gradient and adherence to plates. Cells were submitted to Trypan Blue dye exclusion viability assay, phagocytosis of Zymosan and cell-spreading assays, and quantification of hydrogen peroxide (H2O2) and nitric oxide (NO) production. Monocytes from cattle with PL had the lowest viability (P<0.001), phagocytosis of Zymosan particles (P<0.001), and spreading (P=0.006) rates. Additionally, monocytes from cows with PL had the highest production of H2O2, with no prior stimulus (P=0.001), and after in vitro stimulus with phorbol 12-myristate 13-acetate (P=0.006). Nonetheless, the boost in H2O2 production, provided by in vitro stimulus, observed in monocytes from cows with PL was lower (P=0.015) than that observed in monocytes from SN and AL cattle. There was no difference in NO production among groups. Results show that BLV, despite infecting B lymphocytes, alters innate immune functions of monocytes isolated from BLV-infected cows expressing PL.