SUMMARY
The effect of oxytetracycline (otc) on bovine blood mononuclear cells and neutrophil functions was examined in vitro. Neutrophil functions tested include respiratory burst, peroxidase, and antibacterial activities. Neutrophils were treated with otc (10 to 1,500 μg/ml) before exposure to either opsonized zymosan or bacteria. A dose-response inhibition antibacterial activity to high concentrations of otc (500 to 1,000 μg/ml) was observed. Beginning at a concentration 15 μg/ml, otc treatment of neutrophil lysates resulted in decreased peroxidase activity. A dose response was not observed. In contrast, respiratory burst, measured by nitroblue tetrazolium dye reduction, increased after otc exposure, but only at high concentrations (500 and 1,000 μg/ml) of otc. Mitogen-induced proliferation of blood mononuclear cells cocultured with otc and concanavalin A, phytohemagglutinin-P, or pokeweed mitogen was inhibited at an otc concentration of 100 μg/ml at 48 and 72 hours of culture. These results indicate that blood mononuclear cells are more sensitive to the inhibitory effects of otc than are neutrophils. Furthermore, the otc-mediated inhibition of neutrophil antimicrobial activity is inversely related to the increase in nitroblue tetrazolium reduction. This suggests that otc is uncoupling the hexose monophosphate shunt from production of secreted oxygen radicals. These results also suggest that the peroxidase enzyme system has a large biological reserve capacity.
