Failure to detect integrins of the beta-2 subclass on the human sperm surface

Several cell-to-cell recognition systems utilize the tripeptide Asp-Gly-Arg (RGD) as a cell surface signaling sequence. Mac-1, a member of the integrin subfamily defined by the beta-2 subunit, recognizes C3bi by means of an RGD sequence. Because C3 complement components have been detected on the gamete surfaces and RGD has been demonstrated to be involved in sperm-egg interaction, we explored the possibility that a member of the b2 integrin subfamily was present on the sperm surface and involved in egg recognition. Two methods were utilized to detect integrins on the sperm surface. Sperm were exposed to Mabs directed against different epitopes of each member of this integrin subfamily; and spermatozoa were tested for their ability to bind zymosan or yeast, since Mac-1 bearing cells possess this property. Both methods failed to demonstrate such integrins on the sperm surface, suggesting that another RGD receptor is involved in gamete recognition.