Common Cell Surface Ligands Functioning in Allogeneic Cytotoxic Reaction and Fertilization in Halocynthia roretzi

Two distinct oligosaccharide ligands that function in both the allogeneic contact/cytotoxic reaction (ACR) by hemocytes and gamete fertilization were identified by means of the monoclonal antibodies (Mabs), CRB1 and CRB2, which inhibit both the ACR and fertilization in Halocynthia roretzi. The CRB1 epitope, determined to be the “core” α1–6 fucosylated oligosaccharide epitope (CFOE) in hybrid-type N-glycans, was detected on the cell surfaces of all types of hemocytes as well as on those of follicle cells and the vitelline coat of eggs. The CRB2 epitope, which was indicated as an outer-side sulfated and phosphorylated ojigosaccharide epitope (OSPOE) in complex-type N-glycans, was demonstrated on the cell surfaces of some types of hemocytes and egg follicle cells. Both epitopes, OSPOES and CFOE, may function as ligands in the initial attachment and binding, respectively, in the sperm-egg interaction. These epitopes may also function in the same way in the self-recognition of the ACR. We propose that the fucose residue in CFOE is among the key molecules, and perhaps the most important, involved in self-recognition in the ACR and fertilization.