Opsonization of bacteria by uterine secretions of cyclic mares.

This study analyzes how uterine secretions from mares (female horses) influence the opsonization of the Streptococcus zooepidemicus bacteria, which is consumed by white blood cells during inflammation caused by bacterial infection.

Study Overview

• The research examines the ability of uterine secretions, taken from mares both pre and post bacterial inflammation, to enhance the consumption (opsonization) of Streptococcus zooepidemicus bacteria by white blood cells (polymorphonuclear leukocytes).
• Opsonization is an immune process where pathogens are marked for destruction by immune cells. The research measured this process as the rate of bacterial consumption by immune cells after pre-incubation with the uterine secretions, comparing it with the rate of consumption of unopsonized, non-tagged bacteria.

Experiments and Findings

• The first experiment involved uterine secretions (flushings) taken from four healthy mares with uninfected uteri. No matter the phase of the mares’ menstrual cycle (during estrus or 10 days after ovulation), the flushings did not induce opsonization of the bacteria.
• In the second experiment, a heavy bacterial load (7 X 10⁹ live S. zooepidemicus) was introduced into the uterus of five mares during estrus.
• The flushings taken from the mares at estrus, both before and after inoculation, did not cause opsonization. However, four out of five flushings taken 6 hours post-inoculation demonstrated opsonization capability.

Additional Findings and Conclusion

• Further investigation revealed that in one out of four flushings that had an opsonizing effect, this process was due to a heat-sensitive complement protein, a part of the immune system that enhances the ability of antibodies to clear microbes and damaged cells from the organism.
• The study concludes that the accumulation of opsonins (molecules that enhance the phagocytosis of bacteria by immune cells) in the uterine lumen is part of the acute inflammatory response following bacterial invasion in the mare’s uterus.