B7-H3 promoted sperm motility in humans. 
To determine whether seminal B7-H3 levels are correlated to semen parameters and affect human sperm functions.  A total of 83 healthy donors of proven fertility (aged 22-37 years) and 176 infertile men (aged 21-38 years) were recruited.  Computer-assisted semen analysis and enzyme-linked immunosorbent assay were used to assess the correlations between seminal B7-H3 levels and semen parameters.  Flow cytometry and fluorescence microscopy were used to detect the putative receptor for B7-H3.  Computer-assisted semen analysis and FITC-conjugated pisum sativum agglutinin staining were performed for assessing sperm motility, capacitation, and acrosome reaction (AR) after incubation with various concentrations of B7-H3 for 0-4 hours in vitro.  Seminal B7-H3 level was significantly higher in the healthy donors than that in the infertile men (P <.05), and closely associated with sperm concentrations and progressive motility (all P <.05), but not the other parameters examined (all P >.05).  A putative receptor for B7-H3 was detected on the surface of sperm, with no significant differences in expression between the healthy donors and infertile men (P >.05).  Seminal B7-H3 promoted sperm progressive motility in a time- and dose-dependent manner in vitro, although having no significant influence on sperm capacitation and AR.  B7-H3 showed a favorable effect on human sperm motility, without affecting sperm capacitation and AR.