In vitro studies on the role of seminal plasma proteins on the interaction between polymorphonuclear neutrophils (PMNs) and spermatozoa in the horse

Semen induces a transient uterine inflammatory response in the mare, characterized by an influx of polymorphonuclear neutrophils (PMNs). The physiological role of this inflammation is to clear excess and damaged spermatozoa and bacterial contaminants from the uterus in order to provide an environment that is compatible with normal embryo development and survival. It has been shown that seminal plasma protects spermatozoa from being phagocytosed and destroyed in an inflammatory environment. In addition, previous work has identified the protein fraction in seminal plasma as the component responsible for this effect. The objectives of these studies were to identify and characterize specific seminal plasma protein(s) that are involved in the protection of spermatozoa from PMN binding, and to examine the binding capacity of PMNs when exposed to live or dead spermatozoa and bacteria in the presence or absence of this protein. Secondarily, we examined the interaction between PMNs and spermatozoa in real time. The identity of the protective protein was discovered to be CRISP-3. This protein protects live spermatozoa from binding but did not protect dead spermatozoa or bacteria. Polymorphonuclear neutrophils also exhibit a secondary removal mechanism for dead or damaged sperm cells, through the formation of extracellular traps (NETs). This is the first time a biological function has been described for CRISP-3 in seminal plasma. It is also the first time a selective mechanism in the uterus has been demonstrated and that CRISP-3 functions to protect live sperm cells only.