Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

IV. Acquired Neutrophil Function Defects
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insertion of a polyethylene intramammary device into the
gland cisterns increased the somatic cell count and resulted
in a 75% reduction in clinical mastitis ( Goodger et al. ,
1993 ). Additionally, intramammary administration of soluble
CD14 in coliform mastitis causes binding of endotoxin
and results in recruitment of neutrophils.
Genetic markers have also been associated with susceptibility
to bovine mastitis. Cows with allelic variation in
CXCR2 (i.e., the IL-8 receptor) had increased susceptibility
to mastitis (Rameaud and Pighetti, 2005). Cows with a CC
or GC at CXCR2 777 had decreased neutrophil migration
in response to IL-8 when compared to cows expressing the
GG genotype. Additionally, decreased up-regulation of cell
surface CD18 was observed on neutrophils after stimulation
with IL-8. The results of these studies support a genetic predisposition
to mastitis and further emphasize the importance
of rapid mobilization of neutrophils into the mammary gland
in prevention of infection.
B . Neutrophil Dysfunction in Neonatal
Animals
Neutrophil dysfunction appears to contribute to the susceptibility
of newborn calves and foals to pneumonia, septicemia,
enteritis, and endotoxemia. Reports on neutrophil function
in calves tend to be inconsistent. This is in part due to variation
in the age of the calves, the colostrum status, and the
techniques used to evaluate neutrophil function. For example,
both increased and decreased respiratory burst activity
have been reported in neonatal calves when compared to
adult cows ( Dore et al. , 1991 ; Higuchi and Nigahata, 1998).
Respiratory burst activity in neonates is dependent on the
agonist used. Respiratory burst activity appears to be reduced
when neonatal neutrophils are activated by heat-aggregated
albumin or protein kinase C and enhanced when activated by
opsonized zymosan. This suggests age-related alterations in
cell membrane receptors or differences in intracellular signal
transduction probably involving protein kinase C activity
and tyrosine phosphorylation of cellular proteins (Higuchi
and Nigahata, 1998). Other functional alterations in neonatal
neutrophils when compared to adult neutrophils include
decreased myeloperoxidase and increased alkaline phosphatase
activities, decreased concanavalin A capping, decreased
Fc receptor number, increased chemotaxis, increased aggregation,
and increased shape change ( Zwahlen et al. , 1992 ).
Reports of neutrophil dysfunction in foals are also somewhat
inconsistent. When compared to adult horses, some
reports indicate that foals have no difference in phagocytic
activity, others report decreased phagocytosis when organisms
are opsonized with autologous serum but not when opsonized
with adult serum, whereas yet others state that phagocytosis of
Staphylococcus aureus is decreased when opsonized with
either autologous or adult serum ( McTaggart et al. , 2001 ).
Bacterial killing has been reported to be similar to that of
adult horses in several studies but was found to be reduced in
other studies ( Wichtel et al. , 1991 ). Other neutrophil function
alterations reported in foals include increased random migration,
decreased chemotaxis, decreased iodination, increased
CD18 expression, and the presence of an unidentified serum
factor that suppresses oxidative burst activity.
C . Neutrophil Dysfunction Associated with
Viral Infection
Viral infections have frequently been incriminated as predisposing
food animals to bacterial infections. This effect may,
in part, be mediated by virus-induced neutrophil dysfunction.
The bovine viral diarrhea (BVD) virus is a classic example
of a virus that induces neutrophil dysfunction ( Brown et al. ,
1991 ; Roth et al. , 1981 ). Neutrophils from cows experimentally
infected with cytopathogenic or noncytopathogenic
strains of BVD developed marked impairment of iodination
capacity. Alternatively, other measures of oxygen radical
generation were not altered. Cattle that were persistently
infected with BVD had multiple alterations in neutrophil
function including decreased random migration, decreased
Staphylococcus aureus ingestion, decreased cytochrome
C reduction, decreased iodination, decreased antibodyindependent
cell-mediated cytotoxicity, decreased cytoplasmic
calcium flux, and decreased oxygen radical production.
Another virus incriminated as predisposing cattle to
bacterial pneumonia is infectious bovine rhinotracheitis
(IBR) virus ( McGuire and Babiuk, 1983/1984 ). In an
in vivo study, calves were exposed to an aerosol of IBR
virus and then to an aerosol of Mannheimia haemolytica
5 days later. When compared to calves not exposed to IBR
virus, IBR-exposed calves had delayed neutrophil migration
into the lungs. Neutrophils from IBR-exposed calves
also had decreased random migration and chemotactic
responses. Further, alveolar macrophages had decreased
capacity to produce chemotactic factors. The results of this
study indicate that IBR infection may predispose cattle to
secondary bacterial infections.
Neutrophil function has also been investigated in cats
infected with feline leukemia virus ( Kiehl et al. , 1987 ).
Neutrophil chemotaxis was evaluated in vitro by use of a
modified Boyden chamber apparatus. Cats that were viremic
and clinically ill had lower chemotactic responses
compared to subclinically infected cats. This did not appear
to be a nonspecific effect in that cats that were sick from
other causes did not have reduced chemotactic responses.
D . Effects of Nutrition on Neutrophil
Function
Selenium and vitamin E appear to be important nutrients
in maintaining neutrophil function. As stated previously,