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 Arcanobact erium pyogenes are usually the most prominent bacteria present in bovine ut erine lochial secretions. A. pyogenes alone is rarely found in the course o f a disturbed puerperium. This was confirmed in this study, since average a nd high-grade uterine contaminations were always associated with the presen ce of both bacteria. The contamination grade was positively correlated with uterine polymorphonuclear granulocyte (PMN) numbers and negatively correla ted with blood PMN numbers. Whether E. coil and A. pyogenes affect the phen otype and function of bovine PMN in a similar or differential way was subje ct 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 sec reted bacterial products. Fragments and soluble products differed only quan titatively in their effects on PMN. Usually, long-time exposure (24 h) of P MN to fragments induced the strongest effects. Accelerated death of granulo cytes 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 othe r surface structures remained largely unchanged (MHC class I, CD11c). Funct ional parameters of PMN (phagocytosis; generation of reactive oxygen specie s, ROS; antibody-independent cellular cytotoxicity, AICC) generally decline d after pre-incubation for 24h with products of E. coil or A. pyogenes. Int erestingly, soluble products of A. pyogenes stimulated the phagocytosis of PMN. However, co-incubation with E. coli products abrogated this stimulator y effect. The results supply evidence for similar modes of action of the gr am-negative E. coli and the gram-positive A. pyogenes on bovine PMN. Altera tions 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 act ion of lipopolysaccharide. The dominant functional depression of neutrophil s by E. coli products strengthens the suggestion that the earlier appearanc e of E. coli in the uterus may support the coinfection of this organ by A. pyogenes at later times. (C) 2001 Elsevier Science B.V. All rights reserved .