REGULATION OF UTERINE IMMUNE FUNCTION DURING THE ESTROUS-CYCLE AND INRESPONSE TO INFECTIOUS BACTERIA IN SHEEP

Uterine infections are a major reproductive problem in livestock. We c onducted two experiments to investigate factors that may modulate uter ine responses to infectious bacteria. In Exp. 1, ewes received intraut erine inoculations of either saline or bacteria (75 x 10(7) cfu of Act inomyces pyogenes and 35 x 10(7) cfu of Escherichia coli) on either d 0 or 7 ofthe estrous cycle. Vena caval samples containing uteroovarian blood were collected twice daily from 12 h before until 6 d after ino culation. Only ewes inoculated with bacteria on d 7 developed infectio ns. Basal (4.8 vs .4 pmol), lipopolysaccharide-stimulated (14.2 vs 6.1 pmol), and concanavalin A stimulated (65.8 vs 21.6 pmol) blastogenesi s (i.e., [H-3]thymidine incorporation) of vena caval lymphocytes was g reater (P less than or equal to .002) for ewes inoculated with bacteri a or saline on d 0 rather than on d 7. The number (per 100 white blood cells) of lymphocytes was greater (41.3 vs 30.8, P < .001) and that o f neutrophils was less (42.5 vs 51.6, P < .001) in ewes inoculated on d 0 rather than d 7. Bacteria increased (P < .05) vena caval PGF(2 alp ha) but not PGE(2) concentrations. In Exp. 2, two protein fractions (m olecular weights of greater than or equal to 100 kDa and approximately 12.7 kDa) from chromatography of uterine flushings collected on d 0 o r 7, or 18 d after ovariectomy on d 0 or 7, modulated phytohemagglutin in-stimulated blastogenesis; the heavier fraction from d 0 had a stimu latory component, but the major effects of the fractions were inhibito ry. The differences in immune function and regulation between d 0 and 7 probably explain how the uterus of follicular phase ewes was able to prevent the development of an infection.