Figure 1.

An overview of the origins, components, and main functions of seminal plasma (SP). Seminal plasma makes up more than 95% of the human ejaculate volume, whereas testicular secretions containing spermatozoa compose about 2–5% of semen. Seminal plasma is mainly derived from seminal vesicles, the prostate and epididymis, which produce ~65–75% and ~20–30% of the volume of semen, respectively, with a small proportion generated by bulbourethral glands (~1%). SP is composed of a complicated set of heterogeneous molecular structures, including proteins (enzymes, cytokines, TEX101, ACRV1, TGFΒβ, prostate-specific antigen (PSA), prostatic-specific acid phosphatase (PSAP), etc.), lipids, sugars (fructose), cell-free nucleic acid (DNA, microRNA, and LncRNA), ions (Ca²⁺, Mg²⁺, Zn²⁺, Cu²⁺, etc.), and small-molecule metabolites. In general, SP is a beneficial medium for spermatozoa maturation, nutrition, and motility and modulates spermatozoa function by regulating a cascade of molecular events, such as sperm maturation in the epididymis and capacitation during transport. More importantly, plasma molecules, such as cytokines, directly recognize receptors on epithelial cells lining the cervix and uterus to induce synthesis of pro-inflammatory cytokines and chemokines that recruit and activate inflammatory leukocytes. Besides, SP modulates the release of cytokines and growth factors that regulate embryo development in the oviduct and uterus before implantation, which is critical for early embryo development and implantation.