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The effect on sperm motility of sperm-sperm and sperm-seminal plasma interactions was studied among homologous and heterologous sperm. There were no significant interactions between sperm in vitro, but it was found that seminal plasmas of different donors have different effects on sperm motility, and different sperm react differently to the same seminal plasma. Sperm showed higher motility in a pure physiological solution than when mixed with seminal plasma, even if the plasma and sperm came from the same donor. Various plasma components are responsible for this modulation of sperm motility. It would appear that large numbers of sperm are adaptive, among other things, because they are involved in sperm selection.

In vitro studies have reported that seminal plasma of fertile men has more inhibitory mitogenic effect and higher suppressive activity on antibody-dependent cellular cytotoxicity than seminal plasma from infertile males. Is it possible that variations in the seminal plasma composition could explain these results? The present study was conducted to investigate the relation between immunosuppressive PGE 2 and IL-10 to pro-inflammatory IL-6 in seminal plasma of infertile and fertile men. Utilizing specific ELISA commercial kit, semen samples from 45 infertile undiagnosed and 25 fertile men were examined for the presence of PGE 2 , IL-10, and IL-6. The IL-6 concentration in seminal plasma of infertile men was significantly higher than that of fertile men ( p <.0 4). However, levels of IL-10 were lower for the semen of infertile men than that of fertile men ( p <.04). No differences were observed in PGE 2 concentrations between both groups. Increase in pro-inflammatory cytokines, such as IL-6, and decrease in immunosuppressive ones, such as IL-10, could alter the tolerance to sperm cell in male and female tracts and reduce the favorable conditions to reach the fecundation and implantation. It is necessary to conduct further studies that include other pro- and anti-inflammatory substances to evaluate the importance of the immune balance of semen in human fertility.

Concentrations of tumor necrosis factor- (TNF- ) and interleukin-6 (IL-6) in seminal fluid, as well as levels of sperm lipid membrane peroxidation, were investigated in fertile and infertile men. Semen samples, obtained by masturbation from 37 infertile and 14 fertile men, were examined for the presence of TNF- and IL-6. The level of lipid peroxidation of the sperm membrane was measured by determining malondialdehyde (MDA) formation. The correlation between the IL-6 and the TNF- concentrations in seminal plasma with the levels of lipid peroxidation of the sperm membranes was statistically evaluated. The IL-6 concentration in seminal plasma of infertile men was significantly higher than that of fertile men ( p < .05). Similarly, the level of membrane lipid peroxidation was higher for the semen of infertile men than that of fertile men ( p < .001). A significant positive correlation was found between IL-6 levels in seminal plasma and membrane sperm lipid peroxidation ( p < .002), but not between this parameter and TNF- levels in seminal plasma. These findings suggest a possible association between IL-6 seminal plasma levels and lipid peroxidation of sperm membrane. Stimulation of reactive species production by human sperm and leucocytes, induced by the high levels of IL-6, could explain these results.