Lochial secretions of Escherichia coli- or Arcanobacterium pyogenes-infected bovine uteri modulate the phenotype and the functional capacity of neutrophilic granulocytes.

It has been suggested that in cases of puerperal endometritis of cattle infected with Escherichia coli and Arcanobacterium pyogenes, the neutrophils are compromised in their defense capacity or downregulated functionally. In addition to direct bacterial effects, contents of lochial secretions and secreted products of locally activated polymorphonuclear neutrophilic granulocytes (PMNs) may also account for changes in function of freshly immigrating neutrophils. In this study, lochial secretions were obtained from healthy cows and from cows infected by E. coli or A. pyogenes. Separated uterine PMN of infected cows displayed an altered phenotype and function which correlated with the degree of bacterial contamination. Concurrently tested circulating PMN showed no such changes. Infected lochial secretions sterilized by filtration also changed the phenotype of blood PMN. Lochial secretions of healthy cows displayed only minor effects. The effects on PMN function in infected cows varied: ingestion was less affected, whereas generation of reactive oxygen species (ROS) was severely depressed. Concurrently tested purified bacterial products (solubles and fragments) of E. coli and A. pyogenes did not induce the phenotypical and functional changes observed in blood PMN. Since infected lochia also contained high numbers of immigrated and probably activated PMN, the influence of supernatants from phorbol myristate acetate-activated PMN were tested on freshly isolated blood PMN. Such supernatants also increased the expression of certain surface molecules and inhibited the ROS generation. Thus, reduced function and altered phenotypes of PMN which immigrate into the uteri of cows with bacterial endometritis is due not only to interactions with bacteria or bacterial products, but is also to the uterine milieu.

Influence of Escherichia coli and Arcanobacterium pyogenes isolated from bovine puerperal uteri on phenotypic and functional properties of neutrophils.

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.