Evaluating sperm-polymorphonuclear leukocyte interactions in vitro: The immunomodulatory role of seminal plasma and implications for future ovine studies

The complex anatomical, biochemical and immunological architecture of the ovine cervix presents a substantial barrier to frozen-thawed ram spermatozoa migration following cervical artificial insemination. A key component of the immunological barriers involves interactions between frozen thawed sperm and polymorphonuclear leukocytes (PMN), which are known to infiltrate the female reproductive tract following semen deposition and engage in effector mechanisms, specifically; degranulation, release of neutrophil extracellular traps and phagocytosis. Seminal plasma has been shown to play a critical immunomodulatory role in regulating sperm-PMN interactions across several species, including sheep, reducing sperm-PMN binding in vitro. During in vitro processing and cryopreservation, seminal plasma is inherently diluted, potentially exacerbating immune-mediated clearance of frozen thawed ram spermatozoa. Identifying the specific components of seminal plasma responsible for this immunoprotective effect may inform targeted supplementation strategies. Extracellular vesicles, a heterogenous class of seminal plasma containing proteins, lipids, metabolites and nucleic acids, are also emerging as key mediators of immunological communication. Their potential role in modulating sperm-PMN interactions warrants further investigation to help understand sperm-PMN interactions and implications for improving survival of frozen thawed ram sperm in the cervix following AI.