Effects of susceptibility of mares to endometritis and stage of cycle on phagocytic activity of uterine-derived neutrophils.

Fourteen mares, 7 susceptible and 7 resistant to bacterial endometritis, were used to provide circulating and uterine-derived neutrophils. Uterine neutrophils were recruited by inoculating cell-free filtrates of Streptococcus zooepidemicus, or control vehicle. Mares were assigned to schedules for collection of neutrophils at oestrus or dioestrus. Phagocytic activity of circulating and uterine cells was evaluated by an assay for chemiluminescence after addition of opsonized streptococci. Chemiluminescence generated by circulating neutrophils was greater (P less than 0.05) for susceptible mares (28 +/- 4.9 V) than for resistant mares (13.4 +/- 2.8 V), but was unaffected by stage of cycle or by the interaction. Chemiluminescence by uterine-derived neutrophils from susceptible mares was greater (P less than 0.10) than for resistant mares. There was an interaction (P less than 0.05) with stage of oestrous cycle. Uterine cells from resistant mares in oestrus produced more chemiluminescence than did those from resistant mares in dioestrus (11.5 +/- 4.1 vs 7.1 +/- 2.1 V). The activity of uterine-derived cells of susceptible mares was unaffected by stage of cycle. Susceptibility to endometritis was not associated with a defect in the phagocytic function of uterine neutrophils. Also the function of uterine cells from resistant mares was greater during oestrus than dioestrus.