Sperm-immobilizing antibodies block capacitation in human spermatozoa

Sperm-immobilizing antibodies block human fertilization by interfering with the acrosome reaction (AR). To clarify the mechanism of blockage of AR by sperm-immobilizing antibodies, the authors examined their effect., on the i ncrease of intracellular free Ca2+ concentration induced by follicular flui ds (Ca2+ influx) in spermatozoa and on their capacitation, Sperm-immobilizi ng antibodies did not suppress Ca2+ influx induced by follicular fluid, but they inhibited capacitation of human spermatozoa. Namely Delta %AR (%AR af ter addition of an AR inducer - %AR before treatment) induced by progestero ne was significantly (p < .0001) lower when spermatozoa were incubated in h uman tubal fluid medium cotaining antibody-positive serum (1.2%), compared to that when incubated in control medium (19.2%). Furthermore, the proporti on of both spermatozoa that became capacitated and ones that had become cap acitated decreased significantly (p < .0001) after 2, 4, and 6 h of incubat ion in medium containing antisperm antibody-positive serum, compared to tho se of spermatozoa incubated in control medium. In conclusion, sperm-immobil izing antibodies may be closely related to their blockage of capacitation.