Functional competence and monoclonal antibody reactivity of neutrophils from cows injected with Escherichia coli endotoxin

Neutrophils of cows injected with endotoxin were evaluated for their functional competence and monoclonal antibody binding in relation to morphological maturity. Six clinically healthy lactating Holstein cows were each injected intravenously with 100 μg Escherichia coli endotoxin. Blood was collected at 0, 6, 30, 54, 78 and 150 hours postinjection for total and differential leucocyte counts and to isolate neutrophils for functional assays. Marked leucopenia, neutropenia with left shift to band neutrophils, lymphopenia and monocytopenia were evident at 6 h postinjection. Neutrophil and lymphocyte counts normalised by 30 hours, while band neutrophils remained elevated until 54 hours postinjection. Neutrophils isolated at 6, 30 and 54 hours postinjection revealed significantly increased relative phagocytic index, reduced chemotactic activity, and increased binding of a bovine neutrophil monoclonal antibody (36H10). Ingested bacteria per cell were increased at 6 hours. Phorbol myristate acetate-induced oxidative product formation was significantly reduced at 30 hours, but chemiluminescence activity did not change significantly. In vivo binding of autologous IgG₂ and IgA to neutrophils significantly decreased at 30 and 54 hours and IgM binding was reduced at 78 hours postinjection. Band neutrophils were chemotactically and phagocytically less active than segmented neutrophils. The number of band neutrophils in blood correlated directly with the relative phagocytic index and the percentage of cells binding monoclonal antibody 361110 and inversely with the chemotactic activity of neutrophils. These observations indicate that functional heterogeneity of bovine neutrophils can be attributed, at least in part, to morphological maturity of cells and to differences in expression of surface antigens.