Seminal plasma protects human spermatozoa and pathogenic yeasts from capture by dendritic cells

During the process of fertilization, human spermatozoa are confronted with phagocytic cells of the female reproductive tract. Part of this host mucosal barrier are immature dendritic cells (DCs), which play an important role in the defense of invading microbial pathogens. In the present study, we investigated the potential interaction of spermatozoa with DCs and raised the question of whether seminal plasma impacts the interaction of DCs with spermatozoa or pathogenic microbes.

Flow cytometry and microscopy detected a strong association between spermatozoa and human monocyte-derived DCs, which was partly mediated by the DC-specific adhesion receptor, DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN). Coincubation assays also showed that capture of spermatozoa by DCs was blocked in the presence of increasing concentrations of seminal plasma. This inhibitory effect of seminal plasma was accompanied by altered DC maturation, revealed by flow cytometry analysis of maturation-specific DC surface markers. Phalloidin-staining of the DC cytoskeleton further visualized an impact of seminal plasma on DC morphology. To elucidate the molecular nature of the inhibitory activity of seminal plasma on sperm-DC -association, binding assays were performed in the presence of individual seminal plasma components. This approach identified specific prostaglandins-in particular, PGE₁, 19-OH-PGE₁ and PGE₂, which are present in seminal plasma at high concentrations-as likely inhibitory factors. In contrast to glass beads, the yeast Candida albicans, a common commensal organism and frequent pathogen of the genital tract, was also found to be protected from capture by DCs in the presence of seminal plasma or the specific prostaglandins.

The immunomodulatory power of seminal plasma may help spermatozoa to circumvent the attack of DCs of the female reproductive tract, thereby supporting successful fertilization. At the same time, however, such protective effects of seminal plasma may also modulate DC action during host-pathogen interactions.