FUNCTION OF UTERINE AND BLOOD-DERIVED POLYMORPHONUCLEAR NEUTROPHILS IN MARES SUSCEPTIBLE AND RESISTANT TO CHRONIC UTERINE INFECTION - PHAGOCYTOSIS AND CHEMOTAXIS

In vitro phagocytosis and chemotaxis of uterine and blood-derived poly morphonuclear neutrophils (PMNs) were compared in mares with different resistance to chronic uterine infection (CUI). Both the primary in vi tro function of PMNs and the role of uterine environmental factors on PMN function were investigated. The uteri of mares susceptible to (n = 6) and resistant to CUI (n = 5) were inoculated with 5 x 10(6) Strept ococcus zooepidemicus when the mares were in estrus. Uterine secretion s in addition to uterine and blood-derived PMNs were sampled at 5 and 24 h later. During a subsequent estrus, bacterial inoculation of the u terus was repeated, and samples were removed from the mares 12 and 36 h later. Neither the phagocytic nor the chemotactic capacity of PMNs c hanged over time in any of the groups. However, chemoattractive proper ties of uterine secretions declined over time in both resistant (p < 0 .0007) and susceptible mares (p < 0.01). Significantly higher phagocyt osis (p < 0.03) and chemotaxis (p < 0.05) by uterine derived PMNs were found in the susceptible mares compared to resistant mares when a sta ndardized opsonin (pooled plasma) was used. However, uterine secretion s from susceptible mares demonstrated a poorer opsonizing capacity (p < 0.00002) but were more chemoattractant (p < 0.004) than secretions f rom resistant mares. When opsonins and chemoattractants were provided by plasma, no differences were detected in phagocytosis between blood- derived and uterine PMNs. In contrast, chemotaxis of uterine PMNs were superior to blood-derived PMNs in both resistant (p < 0.007) and susc eptible mares (p < 0.0001) under these conditions. Furthermore, when y east particles were opsonized with uterine secretions, phagocytosis as well as chemotaxis by uterine PMNs was superior to that by blood-deri ved PMNs in both resistant mares (p < 0.0002 for phagocytosis; p < 0.0 0005 for chemotaxis) and susceptible mares (p < 0.04 for phagocytosis; p < 0.00005 for chemotaxis). Uterine secretions demonstrated remarkab ly lower opsonizing and chemoattractant properties when compared to po oled or autologous plasma (p < 0.00005) but were superior to the negat ive control (p < 0.001). It was concluded that phagocytosis but not ch emotaxis of uterine PMNs is impaired i n mares susceptible to CUI. Sin ce uterine PMNs in susceptible mares were demonstrated to be fully fun ctional if given an optimal environment, the cause of the observed dys function is believed to be the result of a negative effect from uterin e secretions on phagocytosis in susceptible mares.