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Abstract
When cows develop endometritis after birth, Escherichia coli and Arcanobacterium pyogenes
are usually the most prominent bacteria present in bovine uterine lochial secretions.
A. pyogenes alone is rarely found in the course of a disturbed puerperium. This was
confirmed in this study, since average and high-grade uterine contaminations were
always associated with the presence of both bacteria. The contamination grade was
positively correlated with uterine polymorphonuclear granulocyte (PMN) numbers and
negatively correlated with blood PMN numbers. Whether E. coli and A. pyogenes affect
the phenotype and function of bovine PMN in a similar or differential way was subject
to in vitro studies. PMN were tested in the presence of washed bacterial fragments
or culture supernatants taken as a source for soluble and/or secreted bacterial products.
Fragments and soluble products differed only quantitatively in their effects on PMN.
Usually, long-time exposure (24h) of PMN to fragments induced the strongest effects.
Accelerated death of granulocytes was only moderately induced by both E. coli and
A. pyogenes products. Both E. coli and A. pyogenes products induced the enhanced expression
of a membrane molecule detected by mAb IL-A110 and of CD11b. Expression of other surface
structures remained largely unchanged (MHC class I, CD11c). Functional parameters
of PMN (phagocytosis; generation of reactive oxygen species, ROS; antibody-independent
cellular cytotoxicity, AICC) generally declined after pre-incubation for 24h with
products of E. coli or A. pyogenes. Interestingly, soluble products of A. pyogenes
stimulated the phagocytosis of PMN. However, co-incubation with E. coli products abrogated
this stimulatory effect. The results supply evidence for similar modes of action of
the gram-negative E. coli and the gram-positive A. pyogenes on bovine PMN. Alterations
in PMN function and phenotype are mainly triggered by direct contact between bacterial
fragments and PMN. Inhibition experiments with polymyxin B demonstrated that E. coli-mediated
effects were not solely due to the action of lipopolysaccharide. The dominant functional
depression of neutrophils by E. coli products strengthens the suggestion that the
earlier appearance of E. coli in the uterus may support the co-infection of this organ
by A. pyogenes at later times.