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 (TNF-α) 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 concentrationdependent
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 IgG2 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
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.
(Am J Vet Res 2000;61:951–959)