The exact cause of sperm antibodies (AsAb) in women is still not well understood, but it is mainly related to the immune response.
Male spermatozoa are an alloantigen (which elicits an immune response) for women. Under normal circumstances, due to the immunosuppressive substances in the seminal plasma of the male semen and the barrier protection of the female reproductive tract, the sperm antigens do not come into direct contact with the immune system of the female body, so anti-sperm antibodies are not normally produced in normal women.
However, under some special circumstances, such as infection or breakage of the female reproductive tract, destruction of the mucosal epithelial barrier, lowering of male seminal plasma immunosuppressants, and coitus during menstruation, the sperm will come into direct contact with B-lymphocytes in the female immune system, leading to the production of anti-sperm antibodies.