PROBLEM: The carbohydrate epitope 3‐fucosyl‐N‐acetyllactosamine (CD15) is a constituent of cell surface glycoconjugates that has been implicated in cell‐cell adhesion mediated by carbohydrate‐specific ligands. The present study was designed to investigate whether CD15 is present on human sperm and whether it plays a role in human sperm‐egg interaction.

METHODS: Fluorescent flow cytometry was used to quantitate the binding of monoclonal antibodies (mAb) to sperm‐bound CD15 and CD46 antigens on acrosome‐intact (AI) and acrosome‐reacted (AR) sperm. The location of the binding site of these mAbs was assessed by fluorescence microscopy. The effects of anti‐CD15 and anti‐CD46 mAbs on gamete interaction were tested utilizing both homologous (human zona binding and penetration) and heterologous (zona‐free hamster egg binding and penetration) systems.

RESULTS: The mean percentage of capacitated sperm which bound anti‐CD15 or anti‐CD46 mAbs was low (4.8% and 5.1%, respectively). Exposure to calcium ionophore A23187 (CaI) resulted in an increase in anti‐CD15 (38.6 ± 4%) and anti‐CD46 (83.4 ± 2%) binding to sperm. Both anti‐CD 15 and anti‐CD46 binding sites were localized by fluorescence microscopy on the sperm acrosomal region. In four experiments, the percent of zona‐free hamster eggs penetrated by human sperm were medium control 93% (62/66), irrelevant mAb 74% (70/94), anti‐CD46 0% (0/107), and anti‐CD15 10% (9/90). One hundred percent (6/6) of human zona were penetrated by human sperm exposed to medium control, 88% (8/9) following exposure to irrelevant mAb, 0% (0/11) following exposure to anti‐CD46, and 50% (5/10) following exposure to anti‐CD 15. The mean (± SD of tightly bound sperm to hamster eggs were medium control 57 ± 18%, irrelevant mAb 64 ± 16%, anti‐CD46 37 ± 13%, and anti‐CD15 19 ± 10%. The corresponding values for human zona were: medium control 118 ± 14%, irrelevant mAb 61 ± 11%, anti‐CD46 39 ± 18%, and anti‐CD15 99 ± 19%.

CONCLUSION: CD15 antigen is expressed on human sperm that have undergone acrosomal loss. mAb to CD15 was shown to inhibit significantly sperm binding and penetration of zona‐free hamster eggs and penetration of human zona pellucida. These findings suggested that sperm‐egg interaction may be mediated in part by the CD15 antigen.

Capsule: Acrosome‐reacted human sperm bind monoclonal antibodies specific for CD15 (Lewis^x) epitope. The binding sites were located on the sperm head. Anti‐CD15 antibody impaired both the binding and penetration of zona‐free hamster eggs and the penetration of human zona by human sperm.