Objective—To determine whether proinflammatory
mediators and glucocorticoids affect CD62L(L-selectin)
expression on peripheral blood neutrophils
from cows in various stages of lactation.
Animals—100 healthy dairy cows during early (13.1 ±
0.79 days after parturition; n = 31), peak (58.7 ± 1.64
days after parturition; 31), and mid (137.2 ± 2.59 days
after parturition; 38) lactation.
Procedure—In vitro effects of relevant proinflammatory
mediators that are released in response to mastitis
caused by gram-negative bacteria such as
lipopolysaccharide (endotoxin), tumor necrosis factor-α, and platelet-activating factor (PAF) on CD62L
expression on bovine neutrophils were assessed by
flow cytometry. Influences of cortisol and dexamethasone
on CD62L expression on bovine neutrophils
were also investigated.
Results—Basal CD62L expression on neutrophils
from cows during early, peak, and mid lactation
were similar. Lipopolysaccharide and tumor necrosis
factor-α had no effect on CD62L expression on
neutrophils from cows at any stage of lactation.
Conversely, PAF elicited a time- and dose-dependent,
down regulatory effect on CD62L expression.
However, no differential shedding of CD62L from
neutrophils of cows at any stage of lactation were
detected. In addition, no effects on CD62L expression
on bovine neutrophils after whole blood incubation
with cortisol or dexamethasone were
observed. Incubation with glucocorticoids did not
prevent the down regulatory effect of PAF on
Conclusions and Clinical Relevance—Comparable
basal CD62L expression on bovine neutrophils and
equal amounts of CD62L shedding from bovine neutrophils
during all stages of lactation suggest that variations
in CD62L density are not a likely cause of susceptibility
of cows to coliform-induced mastitis during
early lactation. (Am J Vet Res 2004;225:1421–1426)
Objective—To evaluate L-selectin (CD62L) and Mac-1
(CD11b) expression at the surface of blood and milk
neutrophils during the early inflammatory response to
Escherichia coli-induced mastitis in cows.
Animals—6 healthy Holstein heifers in early lactation.
Procedure—Blood and milk samples were collected
before and after intramammary administration of
104 CFU's of E coli in the left mammary gland quarters.
Bacterial counts and electrolyte concentrations
in milk, rectal temperature, differential blood
leukocyte counts, milk somatic cell counts, neutrophil
viability, and the expression of CD62L and
CD11b on blood and milk neutrophils were determined
Results—Bacteria grew during the first 6 hours after
inoculation with a pronounced leukocytic influx.
Coincident with neutrophil influx was an increase in
CD62L+ and CD11b+ milk neutrophils, as well as an
improved viability of milk neutrophils. The peak of the
inflammatory reaction was reached approximately 12
hours after E coli inoculation. From that time forward,
changes in CD62L and CD11b expression were
opposed to each other, with a decrease in CD62L
expression and an increase in CD11b expression on
blood and milk neutrophils; the magnitude of the differences
in CD62L and CD11b expression between
blood and milk neutrophils decreased. Percentages of
CD62L+ and CD11b+ milk neutrophils increased to percentages
that were similar to blood neutrophils (ie,
Conclusions and Clinical Relevance—The presence
of adhesion molecules on a large percentage of milk
neutrophils during the acute inflammatory response,
together with the changes in receptor density, suggest
a major role for CD62L and CD11b in neutrophil
function during coliform mastitis. (Am J Vet Res
Objective—To determine whether apoptosis of neutrophils
was accelerated during mastits experimentally
induced by use of Escherichia coli or E coli endotoxin
and whether differences were apparent in the
response to E coli or endotoxin.
Animals—11 healthy lactating Holstein cows.
Procedure—Blood samples were collected from
cows at various intervals after intramammary inoculation
with E coli or endotoxin. Percentage of apoptotic
neutrophils detected after in vitro incubation for 3
hours was determined. Fluorescein isothiocyanatelabeled
annexin-V in combination with propidium
iodide was used to distinguish apoptosis and necrosis
of neutrophils. Total and differential circulating leukocyte
counts and rectal temperature were determined
at the time of collection of blood samples. Milk yield
and milk somatic cell counts were determined at the
time of milking.
Results—Inoculation of endotoxin did not accelerate
in vitro induction of neutrophil apoptosis.
However, inoculation of E coli increased the percentage
of apoptotic neutrophils. At 18 hours after
inoculation, 20% of the neutrophils were apoptotic,
compared with 5% before inoculation. Milk somatic
cell count and rectal temperature increased, milk
production and total leukocyte count decreased,
and percentage of immature neutrophils increased
after inoculation with E coli or endotoxin. However,
kinetics of the responses were more rapid, more
severe, and of shorter duration during endotoxininduced
Conclusions and Clinical Relevance—In vitro induction
of apoptosis of neutrophils was accelerated only
during E coli-induced mastitis and not during endotoxin-
induced mastitis. Endotoxin inoculation as a model
for studying coliform mastitis in dairy cows should be
viewed with caution. (Am J Vet Res 2002;63:448–453)