Characterization of Myeloperoxidase in the Healthy Equine Endometrium.
Authors: Parrilla Hernández Sonia, Franck Thierry, Munaut Carine, Feyereisen Émilie, Piret Joëlle, Farnir Frédéric, Reigner Fabrice, Barrière Philippe, Deleuze Stéfan
Journal: Animals : an open access journal from MDPI
Summary
# Characterization of Myeloperoxidase in the Healthy Equine Endometrium Myeloperoxidase (MPO) has traditionally been viewed as a neutrophil activation marker associated with endometritis, yet it remains consistently present in the uteri of clinically healthy mares—a paradox prompting Belgian researchers to investigate MPO's physiological role in the equine reproductive tract across the oestrous cycle. Using low-volume uterine lavages from 52 mares across oestrus, dioestrus and anoestrus alongside immunohistochemical analysis of 21 endometrial biopsies, the team measured both total and active MPO concentrations and mapped their cellular localisation. MPO concentrations varied substantially across the cycle: markedly elevated during oestrus and anoestrus but significantly suppressed in dioestrus, with the enzyme present predominantly in an enzymatically inactive form throughout all phases. Immunostaining revealed MPO expression concentrated within endometrial epithelial cells, glandular secretions and neutrophils, with maximal expression during oestrus localised to mid and basal endometrial glands, whilst dioestrus showed only sporadic glandular staining and anoestrus displayed minimal luminal epithelial expression. These findings reframe MPO as a constitutive component of the uterine mucosal immune system rather than solely an indicator of pathology, with endometrial cells themselves acting as an active source of the enzyme—a distinction that may refine how practitioners interpret elevated MPO levels and could influence diagnostic thresholds for distinguishing physiological from pathological uterine inflammation.
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Practical Takeaways
- •MPO presence in uterine fluid does not automatically indicate endometritis; baseline MPO levels vary with estrous cycle phase in healthy mares
- •Detection of MPO should be interpreted alongside other clinical and cytological findings when evaluating mare fertility or suspected endometrial disease
- •Understanding physiological MPO expression patterns may improve diagnostic accuracy in distinguishing inflammatory from non-inflammatory uterine conditions
Key Findings
- •Myeloperoxidase (MPO) is constitutively present in uterine lavages of healthy mares across all estrous cycle phases, predominantly in enzymatically inactive form
- •MPO concentrations are elevated during estrus and anestrus but significantly reduced during diestrus
- •Endometrial epithelial cells, glandular cells, and neutrophils are sources of uterine MPO under physiological conditions
- •Maximal MPO immunoexpression occurs during estrus in mid and basal endometrial glands with apical reinforcement