Phagocytosis and killing of Staphylococcus aureus by bovine neutrophils after priming by tumor necrosis factor-α and the des-arginine derivative of C5a

Abstract

Objectives - To evaluate effects of proinflammatory mediators on phagocytosis and killing of Staphylococcus aureus, the oxidative burst (OB), and expression of receptors for opsonins by bovine neutrophils. Sample Population - Neutrophils from 10 cattle. Procedure - Neutrophils were primed with recombinant bovine tumor necrosis factor-α (TNFα) or the des-arginine derivative of bovine C5a (C5adesArg) and mixed with S aureus. Phagocytosis and OB were measured by use of flow cytometry. Rate of phagocytosis and intracellular killing were evaluated. Expression of receptors for immunoglobulins and the C3bi fragment of complement were estimated by use of flow cytometry. Results - Priming of neutrophils by TNF-α improved phagocytosis of S aureus with a concentration-dependent effect. Phagocytosis of preopsonized washed bacteria was increased by activation of neutrophils with C5adesArg. Phagocytosis was optimal when neutrophils primed with TNF-α were activated with C5adesArg. The OB of phagocytizing neutrophils was highest when TNF-α and C5adesArg were used in combination. Bactericidal activity of neutrophils was stimulated by priming with TNF-α or C5adesArg. Binding of bovine IgM or lgG2 to bovine neutrophils was not stimulated by TNF-α, C5adesArg, or both, and aggregated IgG1 did not bind to neutrophils regardless of their activation state. Both TNF-α and C5adesArg increased expression of β2 integrins (CD18), with the highest expression when they were used in combination. Conclusions and Clinical Relevance - The mediators TNF-α and C5adesArg stimulated phagocytic killing by neutrophils and potentiated each other when used at suboptimal concentrations. Bovine neutrophils have enhanced bactericidal activities at inflammatory sites when TNF-α, C5adesArg, or both are produced locally.