Respiratory burst activity in activated and unstimulated isolated bovine blood neutrophils during experimentally induced Escherichia coli mastitis

The respiratory burst activity, measured as H2O2 production, of isolated bo vine polymorphonuclear leucocytes (PMN) was evaluated during experimentally induced Escherichia coli mastitis by means of flow cytometry in cells acti vated by phorbol 12-myristate 13-acetate (PMA) and in unstimulated cells. A s expected, a significantly reduced respiratory burst activity was observed in PMA-activated PMN 18 h after intramammary inoculation with Escherichia coli. At this time only 75% of the PMA-activated PMN showed a respiratory b urst, but with a higher intensity than that measured before and later after infection with Esch. coli. In addition, an increase in the respiratory bur st activity was observed in unstimulated blood PMN during a short period at 18 h after infection, when up to 30% of the unstimulated PMN had a respira tory burst activity. The increase in the respiratory burst intensity of PMA -activated PMN and the spontaneously augmented production of reduced oxygen species by the unstimulated PMN during infection with Esch. coli might ind icate the production of a natural stimulator of burst activity in circulati on, most probably originating from the inflamed udder.