Cellular and humoral responses to intrauterine inoculation with viable Streptococcus zooepidemicus in a group of mares with varying resistance to endometritis

This thesis records in part the search for a technique to identify mares with lowered resistance to Streptococcal endometritis. It also presents the findings of studies on the pathogenesis of equine Streptococcal endometritis, including the factors influencing the elimination of the experimentally infused Streptococcus zooepidemicus. Acute endometritis was induced in 32 mares, which were classified as either resistant (21) or susceptible (11) to endometritis depending on their breeding histories and the degree and extent of endometrial pathology. Infection was induced by intrauterine inoculation of 10^9 viable S. zooepidemicus suspended in 2 mis of sterile isotonic mannitol solution. Three control mares were infused with 10 mis of sterile isotonic mannitol. Serial uterine swabs, washings and biopsies and blood samples were obtained before (0 hrs), and at fixed time intervals after intrauterine infusion of the Streptococci inoculum (2, 3, 4, 6, 9, 12 and 15 hrs and 1, 2, 4, 6, 10, 14 and 28 days). The findings of physical examination and the results obtained from the serial samples were used to assess the degree, extent and duration of the inflammatory reaction and immune response, endometrial damage and the persistence of the infused Streptococci in the uterus. The major findings of the present study were:- 1) A predominantly neutrophilic response, which did not differ significantly between resistant and susceptible mares was observed within 2 hours of challenge. Neutrophil function tests indicated that there were no significant differences in the chemotactic. phagocytic and intracellular killing ability of both circulating and uterine neutrophils obtained from resistant and susceptible mares. Uterine washings obtained before and after challenge from both resistant and susceptible mares did not enhance phagocytosis. 2) An influx of serum proteins including immunoglobulin A, G, G(T) and traces of M, which reached a peak between 6 and 24 hours of challenge, was observed in all challenged and control mares. IgA and IgG concentrations in uterine washings obtained from the challenged mares, were significantly higher than those measured in uterine washings obtained from control mares. This finding and the observation that persisting infection resulted in continuing high levels of IgA indicated that the IgA was produced in response to the infused Streptococci. There was, however, no significant difference between the total protein concentrations in uterine washings and fluid obtained from resistant and susceptible mares. The concentrations of ceruloplasmin and alfa 2 - globulins, both documented modulators of inflammation, reached their highest levels between 6 and 24 hours after challenge. In contrast the concentrations of trypsin inhibitors, (also documented modulators of inflamination), remained unchanged throughout the observation period. 3) The stage of the oestrous cycle at challenge was determined using plasma progesterone levels (measured by the enzyme immunoassay (EIA)), clinical and physical examination findings and histological findings in uterine biosies obtained 10 days after challenge, available from the present study indicated that the stage of the oestrous cycle at challenge did not influence the response to Data Streptococcal challenge or the persistence of infection. 4) Light and electron microscopic studies showed that the degree and extent of cellular infiltration into the endometrium and the extent of uterine luminal epithelial damage after challenge was similar in both resistant and susceptible mares. From the data obtained in the present investigations it was concluded that repeated uterine infections, in mares with lowered resistance to endometritis (susceptible), occured in the presence of IgA and that although these mares were capable of subsequently mounting a local immune response that was comparable to that mounted by the resistant mares, they were still unable to eliminate the infused Streptococci. This inability to resolve the experimentally induced endometritis was, however, not due to gross disorders in neutrophil function, lack of immunoglobulins or natural modulators of inflamination and neither was it dependent on the stage of the oestrous cycle at challenge