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 (FT) ram spermatozoa migration following cervical artificial insemination (AI). A key component of the immunological barriers involves interactions between FT sperm and polymorphonuclear neutrophils (PMN), which are known to infiltrate the female reproductive tract (FRT) following semen deposition and engage in effector mechanisms, specifically degranulation, release of neutrophil extracellular traps (NETs) and phagocytosis. Seminal plasma (SP) 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, SP is inherently diluted, potentially exacerbating immune-mediated clearance of FT sperm. Identifying the specific components of SP responsible for this immunoprotective effect may inform targeted supplementation strategies. Extracellular vesicles (EVs), a heterogenous class of SP-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 FT ram sperm in the cervix following AI.