Opsonization of bacteria by uterine secretions of cyclic mares

Uterine flushings collected from mares before and after bacterial-induced inflammation were assayed for ability to opsonize Streptococcus zooepidemicus for phagocytosis by polymorphonuclear leukocytes. Opsonization was measured as the peak phagocytic rate of bacteria preincubated with uterine flushings relative to the peak phagocytic rate of unopsonized bacteria. Flushings from four mares with noninfected uteri were unable to opsonize bacteria regardless of whether uteri were flushed at estrus or on day 10 postovulation. In a second experiment, 7 X 10(9) live S. zooepidemicus were inoculated into the uterus of five mares during estrus. Uterine flushings collected at the estrus before inoculation or at the estrus after inoculation did not opsonize bacteria. Four of five flushings collected 6 hr post inoculation, however, were capable of opsonization. Based on heat inactivation at 56 degrees C, the opsonizing activity of one of four flushes was due to a complement protein. It was concluded that one aspect of the acute inflammatory response of the mare's uterus is accumulation of opsonins in the uterine lumen.