Analysis of Fibronectin on Human Sperm

PURPOSE: The purpose of this study was to localize fibronectin on human sperm and correlate its distribution with the morphological and functional integrity of sperm. MATERIALS AND METHODS: Semen samples were collected and sperm fractionated by swim-up. Subsets of the swim-up sperm were capacitated and acrosome reacted. Damage to swim-up sperm was induced by freezing and thawing. The presence of fibronectin on the surface of sperm was determined by immunocytochemistry. RESULTS: FN immunoreactivity was variable but staining on the sperm tail was consistently highest, whereas FN immunoreactivity over the acrosome and equatorial band was consistently lowest. Capacitation and acrosome reaction did not substantially change the distribution of FN staining. However, swim-up sperm had significantly less FN immunoreactivity (4%) than sperm that were unable to swim-up (12%; p < 0.01). Sperm that were deliberately damaged by freeze/thaw showed significantly increased FN binding (p < 0.01). FN immunoreactivity was inversely correlated with sperm viability (r = -0.68), motility (r = -0.70), and morphology (r = -0.63). CONCLUSIONS: This study demonstrates that only a minority of the sperm in an ejaculate stain positive for FN and the localization of FN in positive sperm is primarily to the tail. Inferior sperm stain more frequently for FN leading to an inverse correlation between FN staining and sperm quality. Taken together, these results do not support a role for FN in sperm-egg binding. However, FN staining may provide a method for selecting the highest quality sperm for use in assisted reproduction techniques.