Variability in human semen content and its potential effects in the female reproductive tract

Abstract

Human semen is a complex medium containing high concentrations of cytokines, chemokines, and growth factors that play key roles in orchestrating immune responses during reproduction. These factors are essential to establishing conditions that facilitate fertilization and embryogenesis through modulation of local immune responses in the female reproductive tract. Typically, semen initiates a biphasic process of inflammation that is gradually resolved, leading to immune cell recruitment pivotal to clearing excess sperm and establishing tolerance of the fetal allograft. However, the identity and concentration of factors found in semenmay be altered in the male reproductive tract as a consequence of sexually transmitted infections and infertility conditions. As a result, imbalances in semen content can skew the secretory response of the cervicovaginal epithelium after deposition during heterosexual intercourse, which may distort local immune activity and lead to embryo rejection or enhanced pathogen transmission. Recognizing the array of factors contained in semen and the degree to which they vary is an essential part of understanding the impact of variations in semen content on reproductive biology and the transmission of sexually transmitted disease pathogens.