Procoagulant tissue factor-exposing vesicles in human seminal fluid

Recent studies indicate that various types of vesicles, like microparticles (MP) and exosomes, are present in blood, saliva, bone marrow, urine and synovial fluid. These vesicles, which are released upon activation or shear stress, are thought to play a role in coagulation, neovascularisation, inflammation and intercellular signalling. Seminal fluid is a cell-, sperm- and protein-rich suspension. Although seminal fluid is known to contain vesicles like prostasomes, MP and exosomes have never been characterised. Therefore, the aim of our study was to analyse and characterise vesicles in seminal fluid in male partners of patients undergoing controlled ovarian stimulation for IVF/ICSI. MP from seminal fluid of patients during routine IVF/ICSI procedures were detected and analysed with flow cytometry (FACS) and transmission electron microscopy (TEM), using antibodies against tissue factor (TF), CD10, CD13, CD26 and annexin V. The coagulant properties of vesicles were studied using a fibrin generation test. MP were detected in human seminal fluid by both flow cytometry and TEM. Seminal fluid-derived MP expressed CD10, CD13, CD26 and TF, which was highly procoagulant and a powerful trigger of the extrinsic pathway of coagulation. The extent to which the procoagulant activity of MP in seminal fluid contributes to the implantation process itself and therefore affects human reproduction needs to be further elucidated.