Bovine neutrophils recruited by endotoxin to a teat cistern continuously produce oxygen radicals and show increased phagocytosis and extracellular chemiluminescence.

Bovine neutrophils were harvested from a teat cistern following endotoxin infusion and were compared with blood neutrophils by measurements of chemiluminescent and phagocytic activity towards C3- and IgG-opsonized and unopsonized yeast particles. Both phagocytosis and luminol-dependent chemiluminescence elicited by all three particles were enhanced in the teat cells. The increase in the luminol-dependent chemiluminescence towards C3- and IgG-opsonized particles was due to an enhanced extracellular release of myeloperoxidase. The observed increase in phagocytosis of unopsonized yeast was shown to reflect the interaction between up-regulated CR3 receptors on the surface of the teat neutrophils and the yeast particles. A high chemiluminescent activity of the teat neutrophils in both the luminol- and lucigenin-dependent systems in the absence of a phagocytic prey indicated that the NADPH oxidase was permanently active and that myeloperoxidase was continuously released by the cells. Treatment of neutrophils with cytochalasin B showed that the chemiluminescence and phagocytosis of teat neutrophils were less sensitive to this drug than that of blood neutrophils. These results indicate that the teat neutrophils have up-regulated their receptors for IgG- and C3-opsonized and unopsonized yeast on the cell surface by the action of actin. The cells also have a permanently active NADPH oxidase dependent on the association with actin and show a higher tendency than blood neutrophils to secrete the content of their primary granules during phagocytosis.