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

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Chapter | 11 Neutrophil Function
oxygen radical generation. Although the mechanism of this
suppression is unknown, both the membrane-bound and
cytoplasmic components of NADPH oxidase appear to be
down-regulated in infected neutrophils.
Yersinia enterocolitica blocks phagocytosis by neutrophils
and macrophages. Tight binding of the organism
to cell membrane receptors of these cells causes a local
decrease in extracellular calcium that results in uptake of
TTSS and Yop proteins from the organism into the cytosol.
Yop H is a tyrosine phosphatase that targets SH2 domains
and prevents increases in intracellular calcium necessary
for phagocytosis and degranulation. Mutant bacteria
lacking Yop H are rapidly phagocytized and cleared by
phagocytes.
Salmonella spp . have several virulence factors ( Roos
et al. , 2003 ). Spi-1 encodes proteins that are secreted
into cells and modulate the actin cytoskeleton. This leads
to uptake of the organism into a membrane-bound vacuole
within the cell. Once in the target cell, the Spi-2 gene
cluster promotes bacterial survival. These proteins interfere
with formation of the NADPH oxidase complex thus
reducing the generation of oxygen radicals.
Shigella invade the colonic mucosa and are engulfed
by macrophages and epithelial cells. Shigella contain virulence
factors IpaB and IpaC that enable them to escape
from phagosomes of both macrophages and epithelial cells.
However, elastase within neutrophils selectively degrades
IpaB and IpaC, which prevents escape of the organism
from the phagosome and facilitates organism killing.
Mycobacteria enhance their survival within phagocytes
primarily by inhibiting fusion of late endosomes
and lysosomes with the phagosome ( Peyron et al. , 2001 ).
As a result, phagosomes fail to obtain markers of maturation
including Rab7, LAMP-1, and LAMP-2 ( Fig.
11-3 ). This process has been most studied in macrophages.
Mechanisms responsible for the arrest of phagosome
maturation are complex and involve both host and organism
factors. Coronin 1, also termed tryptophan-aspartatecontaining
coat protein (TACO), has been identified as
being involved. Coronin 1 is a member of a family of
proteins involved in actin-cytoskeletal remodeling and
phagocytosis as well as other cell functions. In murine
macrophages, coronin 1 is retained on the phagosomes of
macrophages infected with live mycobacteria, whereas it
rapidly dissociates from phagosomal membranes of dead
mycobacteria ( Tailleux et al. , 2003 ). Mycobacteria appear
to be able to arrest phagosome maturation by depleting the
phosphatidylinositol 3-phosphate (PI3P) content within
the phagosomal membrane ( Hmama et al. , 2004 ). PI3P is
synthesized in early endosome and phagosome membranes
and functions as a membrane-trafficking regulatory lipid
essential for phagolysosome biosynthesis. This effect may
be mediated by glycosylated phosphatidylinositol lipoarabinomannan
derived from the cell wall of pathogenic
mycobacterial organisms ( Hmama et al. , 2004 ).
IV . ACQUIRED NEUTROPHIL FUNCTION
DEFECTS
A . Neutrophil Dysfunction in Periparturient
Dairy Cattle
Numerous studies have documented neutrophil dysfunction
in periparturient dairy cattle. Significantly decreased
random migration, iodination, and chemiluminescence
of neutrophils were observed 1 week after parturition
( Kehrli et al. , 1989 ). In another study, a decrease in neutrophils
oxidative burst activity was observed 1 to 3 weeks
after calving ( Dosogne et al. , 1999 ). This was related to a
pregnancy-associated glycoprotein in the blood.
The cause of periparturient neutrophil dysfunction is
incompletely understood. Selenium concentrations in periparturient
cattle may be a significant factor in predicting
neutrophil function. Neutrophils from postparturient dairy
cows with relatively high blood selenium concentrations had
greater superoxide production and greater potential to kill
bacteria when compared to cows with relatively low selenium
concentrations ( Cebra et al. , 2003 ). Excessive glucocorticoid
production may also be involved in the neutrophil
dysfunction. In a study in which microarrays and real-time
RT-PCR techniques were used to study neutrophils from
periparturient and glucocorticoid-treated cattle, similar functional
alterations were observed ( Burton et al. , 2005 ).
Altered neutrophil function and recruitment to the
mammary gland have been incriminated as a factor in the
increased incidence of mastitis during the periparturient
period ( Kehrli et al. , 1989 ; Paape et al. , 2003 ). In general,
milk neutrophils are less effective than blood neutrophils
in phagocytizing and killing bacteria ( Paape et al. , 2003 ).
This has been attributed to the lower energy reserve of
milk neutrophils and phagocytosis of milk fat globules
and casein. Lysosomes fuse with phagosomes containing
milk-fat globules and casein thus reducing the number
available to fuse with phagosomes containing bacteria.
Milk has been reported to reduce the capacity of neutrophils
to phagocytize bacteria three-fold. ( Paape et al. ,
1981 ). A negative correlation has been reported between
the capacity of milk to support neutrophil phagocytosis
and clinical mastitis ( Paape et al. , 2003 ). In another field
study of 70 lactating dairy cows, decreased milk neutrophil
chemiluminescence activity was associated with susceptibility
to mastitis caused by S. aureus ( Piccinini et al. ,
1999 ). This relationship indicates that neutrophil oxidative
burst activity may play a major role in preventing mastitis.
Additionally, postparturient cows have a reduced capacity
to recruit neutrophils into the mammary gland during coliform
mastitis ( Shuster et al. , 1996 ).
Neutrophil recruitment appears to be a critical determinant
of resistance to mastitis. Several studies have
documented that increasing the milk somatic cell count is
highly effective in preventing mastitis. In one field trial,