Sperm-specific isoantibodies and autoantibodies inhibit the binding of human sperm to the human zona pellucida

Heterologous antisperm antibodies induced by immunization with Freund's adjuvants are known to inhibit sperm-zona binding. The authors have tested whether spontaneously occurring sperm-directed isoantibodies and autoantibodies inhibit the binding of human sperm to the human zona pellucida. Zonae pellucidae were obtained from the ovaries of a woman of reproductive age undergoing surgery for uterine malignancy. Couples at risk for immunity to spermatozoa were screened for humoral antisperm antibodies by immunobead binding. Sera containing head-directed antibodies of IgA and/or IgG classes were selected for passive antibody transfer. Populations of spermatozoa exhibiting differing proportions of antibody-bound sperm were obtained by exposure of antibody-negative sperm of a fertile donor to untreated sera or sera depleted of head-directed antisperm antibodies by prior absorption. Each zona pellucida was challenged sequentially with two populations of sperm. An inverse relationship was found between the number of spermatozoa adherent to the zona and the proportion of sperm exhibiting binding of IgA or IgG immunoglobulins over the head, indicating that the presence of these antibodies in the acrosomal region of the sperm head inhibited their ability to attach to the zona pellucida.