Characterization of human sperm antigens reacting with anti-sperm antibodies from an infertile female patient's serum.

Identification of sperm antigens that elicit immunoglobulin (Ig) production and knowledge of their roles in sperm transport and fertilization may enhance diagnosis and treatment of immunologic infertility. Sperm antigens recognized by a female patient's serum anti-sperm antibodies were characterized using an indirect immunobead-binding test, immunoblot analysis, and immunochemical labeling. The anti-sperm antibodies' effect on sperm function was evaluated by acrosome induction by calcium ionophore. Immunobeads specific for IgG were bound to the head of 79% of motile donor sperm. Immunochemical labeling of antibody-binding sites was restricted to the plasma membrane over the acrosomal crescent. No labeling was observed on the inner acrosomal membrane of acrosome-reacted sperm. The antibodies reacted with 35-, 40-, 47-, and 65-kd proteins extracted from acrosome-intact donor sperm. Sperm incubated in 1:4, 1:8, 1:16, and 1:32 dilutions of anti-sperm antibody-positive serum had similar rates of spontaneous acrosome reaction and significantly lower rates of ionophore-induced acrosome reaction compared with sperm incubated in control serum. These results suggest that sperm antigens recognized by the patient's serum anti-sperm antibodies are restricted to the acrosomal region of the plasma membrane. The antibodies may impair fertility by compromising the sperm's ability to undergo capacitation and/or acrosome reaction.