The fertilizing ability of human epididymal sperm.

PURPOSE: Membrane cofactor protein (MCP), CD46, whose primary function is to protect host cells from homologous complement, has been presumed to serve as a sperm adhesion molecule for oocytes. The purpose of this study was to clarify the relationship between the properties of MCP expressed on epididymal sperm and their fertilizing ability in a recently developed strategy for assisted reproduction.

METHODS

We collected ejaculated sperm from normal subjects and epididymal sperm from vasectomized subjects and patients with congenital absence of the vas deferens. Western blotting and cofactor activity assay were performed to investigated the structural and functional properties of MCP.

RESULTS

Epididymal spermatozoa which showed a reduced fertilizing ability tended to react poorly with antibodies against MCP and also showed low cofactor activity, indicating weak complement regulatory activity compared to that of ejaculated spermatozoa.

CONCLUSIONS

MCP is sufficiently expressed in ejaculated sperm in men with a normally developed epididymis but is diminished in epididymal sperm from men with congenital or acquired obstruction of the vas deferens.