Epitope analysis for human sperm‐immobilizing monoclonal antibodies, MAb H6‐3C4, 1G12 and campath‐1

Human monoclonal antibody, MAb H6‐3C4, possesses strong sperm immobilizing activity. MAb H6‐3C4 has been suggested by several research groups to react with a carbohydrate moiety of male reproductive tract CD52 (mrtCD52). In the present study, we analysed the epitope on mrtCD52 for MAb H6‐3C4 and found that it was polymorphic in Western blot analysis and disappeared after enzymatic removal of the N‐linked carbohydrate moiety. Two other monoclonal antibodies (1G12, campath‐1) with sperm‐immobilizing activity recognized mrtCD52 in a polymorphic manner similar to MAb H6‐3C4. Further analysis showed that 1G12 recognized a structure formed by the peptide and/or a glycosylphosphatidylinositol (GPI) anchor portion as does campath‐1. Results of a lectin binding assay suggested the presence of O‐linked carbohydrates on mrtCD52. Our results also indicated that the peptide portion of CD52 could serve as an epitope for sperm‐immobilizing antibodies. It was concluded that the epitope of MAb H6‐3C4 is similar to, but distinct from, those of 1G12 and campath‐1, and that mrtCD52 contains different antigenic epitopes.