Presence and Incidence of Izumo Antibodies in Sera of Immunoinfertile Women and Men

Abstract

Sperm antigens that are relevant to fertilization and fertility, and are involved in human immunoinfertility, are being investigated in several laboratories. Izumo is a sperm-specific protein that has shown to be essential for sperm-egg fusion. The present study was conducted to examine the expression of Izumo protein in human sperm. Also, the presence and incidence of Izumo antibodies in sera of immunoinfertile women and men were investigated. The expression of Izumo protein in human sperm was examined by the Western blot procedure. Sera from immunoinfertile women (n = 25) and fertile women (n = 23), as well as sera from immunoinfertile men (n = 20) and fertile men (n = 15), were collected and analyzed for immunoreactivity with Izumo peptides in the enzyme-linked immunosorbent assay (ELISA). Three epitopes of human Izumo, namely one epitope of Izumo1, and two epitopes of Izumo2 [Izumo2 (K-15), and Izumo2 (T-17)], respectively, were selected for the present study. In the Western blot procedure, the Izumo1 antibody recognized a specific protein band of ~39 kDa in human sperm extract. In ELISA, 56% of the immunoinfertile female sera reacted positively (≧3 S.D. units) with Izumo1, 40% with Izumo2 (K-15), and 20% with Izumo2 (T-17) peptide. None of the sera (0%) from fertile women reacted positively (≦3 S.D. units) with any of the three Izumo peptides. None of the sera from immunoinfertile (0%) or fertile men (0%) reacted positively with any of the three Izumo peptides. Our findings indicate that human sperm expresses Izumo protein, and the immunoinfertile female sera have circulating isoantibodies against this protein. This is the first study to our knowledge, which examined the presence and incidence of Izumo antibodies in female and male immunoinfertility. These findings may find clinical applications in specific diagnosis and treatment of infertility, and contraceptive vaccine development.