Isolation and identification of sperm membrane antigens recognized by antisperm antibodies, and their possible role in immunological infertility disease

Antisperm antibodies (ASA) are the main cause of immunological infertility, as they impair sperm function by binding to the sperm membrane. In this study, we isolated highly enriched sperm membrane proteins by two-dimensional (2D) gel electrophoresis. Isoelectric focusing, as a first dimension, was performed on precast DryStrip IPG 4-7. The second dimension was carried out on 12% sodium dodecyl sulphate-polyacrylamide gels. A total of 18 antigens were identified by the subsequent 2D Western blotting using ASA from seminal plasma samples of infertile patients. Six of the recognized proteins were isolated and analysed by means of mass spectrometry and peptide matching. They were identified as heat shock proteins HSP70 and HSP70-2, the disulphide isomerase ER60, the inactive form of caspase-3 and two subunits of the proteasome (component 2 and zeta chain). The biochemical identification of these proteins will be helpful in understanding the mechanisms by which ASA impair both sperm function and fertilization. Thus, these proteins may also be useful in the development of reliable methods for ASA detection.