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

The respiratory burst activity, measured as H 2 O 2 production, of isolated bovine polymorphonuclear leucocytes (PMN) was evaluated during experimentally induced Escherichia coli mastitis by means of flow cytometry in cells activated by phorbol 12-myristate 13-acetate (PMA) and in unstimulated cells. As 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 burst, but with a higher intensity than that measured before and later after infection with Esch. coli. In addition, an increase in the respiratory burst 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 respiratory 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 indicate the production of a natural stimulator of burst activity in circulation, most probably originating from the inflamed udder.