The influence of mononuclear leukocytes on the chemotactic responsiveness of polymorphonuclear leukocytes of bovines

Polymorphonuclear leukocytes (PMN) isolated from the blood of bovines which do not react with an influx of cells into the milk upon intramammary administration of low doses of endotoxin (Group II), show a diminished chemotactic activity in vitro as compared to PMN of bovines which do respond to intramammary endotoxin administration (Group I; 8). The purpose of the present study was to determine whether other immune cells affected the chemotactic activity of PMN of Group I and II bovines. Mononuclear leukocyte suspensions of Group I animals had no effect on the migration of PMN of Group I animals. In contrast, the distance migrated by Group II PMN was diminished in the presence of Group II mononuclear leukocytes. As a consequence, this phenomenon resulted in a much larger difference in chemotactic activity of PMN in vitro between Group I and Group II bovines. It can be concluded that the chemotactic activity of PMN of animals which are more susceptible for mastitis as indicated by non-responsiveness to intramammary endotoxin-infusions, was further down-regulated by mononuclear leukocytes.