Effect of Long-term Hyperimmunization on the Presence of Mast Cells in the Endometrium of the Mare

• Mast cells (MC) presence in the endometrium of hyperimmunized mares were analyzed.
• MC infiltration of endometrium after immunological stimulation was observed.
• Connection between MC occurrence and endometrosis process in the mare was proposed.

Because of their ability to synthesize and secrete neurohormones, mast cells (MCs) are classified as paraneurons. One of the processes influenced by MCs is fibrosis, which plays a crucial role in endometriosis in mares. The aim of the present study was to determine the dynamics of MC occurrence in the endometrium of mares that were subjected to long-term hyperimmunization with the focus on its possible correlation with the endometriosis. The experimental group of seven draft mares, 6 to 11 years old, was subcutaneously hyperimmunized every 7 days with 200 mL of bacterial broth culture of Erysipelothrix rhusiopathiae for the duration of the experiment (20 months). The endometrial biopsy was taken from all mares 1 day before the first immunization (time point 0) and 5, 10, and 20 months after the start of the immunization protocol (time points 1, 2, and 3, respectively). Endometrial samples were evaluated according to Kenney and Doig classification, and MC number was counted. Statistical analysis of the MC numbers showed that differences between time point 0 and time points 2 and 3, and between time point 1 and time points 2 and 3 were statistically significant (P < .001). Parallel in six mares significant increase in endometriosis process was observed. Those result showed that long-term hyperimmunization triggered proliferation of endometrial MCs and endometriosis process. Considering long-lasting antigenic stimulation as a model of chronic disease with MC activation, it could be speculated that MC-induced fibrosis represent one of possible mechanisms involved in development of endometriosis in mares.