A new model system for endometritis: Basic concepts and characterization of phenotypic and functional properties of bovine uterine neutrophils

Abstract

The intention of this study was to develop a model system of puerperal endometritis in cows, which would permit detailed analysis of components and mechanisms relevant to the onset and development of this disease. As the first essential step we examined the induction and migration of polymorphonuclear neutrophil granulocytes (PMNs) into the uterus under defined conditions. Migration of neutrophils into the uterus of healthy estrus synchronized heifers (n = 8) was induced by intrauterine infusion of 50 ml of a 30 nmol/l solution of leukotriene B 4 (LTB 4). Before and 24 h after the infusion, cells were flushed from the uterine lumen. In addition to total leukocyte counts, viability and morphological differentiation of various leukocyte populations, phenotypic characteristics of PMNs were monitored by means of quantitative immunofluorescence using monoclonal antibodies. The capacity of PMNs to generate reactive oxygen species (ROS) following activation with phorbol ester was measured using dihydrorhodamine 123. The phagocytic activity of PMNs was determined by their ingestion of fluorochrome labeled nonviable staphylococci. Most methods mentioned above were adapted to flow cytometric analysis. The LTB 4 attracted selectively large numbers of PMNs into the uterus. In comparison with contemporarily harvested blood PMNs, neutrophils recovered from the uterine lumen showed changes in the expression of some but not all of their surface structures. Phagocytic activity of uterine PMNs was significantly lower when compared with that of blood PMNs. In contrast, the generation of ROS was not different between blood and uterine PMNs. Thus, the concept of inducing endometritis directly by local application of a physiological mediator of inflammation such as LTB 4 has been successful. This bovine model permits detailed analysis of migration of PMNs into the uterus and their behavior under defined conditions within the autologous system.