The respiratory burst activity, measured as H2O2
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.