Inhibition of fertilization by a monoclonal antibody recognizing the oligosaccharide sequence GalNAc beta 1----4Gal beta 1----4 on the mouse zona pellucida

Mouse eggs and pre-implantation stage embryos express on their surfaces a carbohydrate epitope, TEC-2, defined by an IgM monoclonal antibody, TEC-02. The TEC-2 epitope involves the oligosaccharide sequence GalNAc beta 1---4Gal beta 1---4 that is expressed on the plasma membrane and zona pellucida of mouse eggs and on a very limited number of other cell types. In this study we addressed the question whether or not the binding of TEC-02 antibody to the mouse eggs would interfere with their fertilization. Our data showed that the TEC-2 epitope is carried by two zona pellucida glycoproteins, ZP2 and ZP3. Binding of TEC-02 antibody to mouse eggs inhibited specifically and in a dose-dependent manner their fertilization in vitro. The inhibitory effect of TEC-02 antibody was dependent on the presence of an intact zona pellucida. Direct radioantibody binding assays indicated that the TEC-02 antibody completely inhibited fertilization at a concentration at which one quarter of all available TEC-2 binding sites was occupied. Binding of TEC-02 antibody to an egg did not interfere with initial attachment of the sperm to the egg but inhibited maintenance of sperm binding to the zona pellucida, the secondary binding. The combined data indicate that TEC-2, which is a well-defined zona pellucida specific carbohydrate epitope, might be a part of the secondary sperm receptor.