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 effects on the increase of intracellular free Ca 2+ concentration induced by follicular fluids (Ca 2+ influx) in spermatozoa and on their capacitation. Sperm-immobilizing antibodies did not suppress Ca 2+ influx induced by follicular fluid, but they inhibited capacitation of human spermatozoa. Namely &#106 %AR (%AR after addition of an AR inducer - %AR before treatment) induced by progesterone was significantly ( p <. 0001) lower when spermatozoa were incubated in human tubal fluid medium cotaining antibody-positive serum (1.2%), compared to that when incubated in control medium (19.2%). Furthermore, the proportion of both spermatozoa that became capacitated and ones that had become capacitated decreased significantly ( p <. 0001) after 2, 4, and 6 h of incubation in medium containing antisperm antibody-positive serum, compared to those of spermatozoa incubated in control medium. In conclusion, sperm-immobilizing antibodies may be closely related to their blockage of capacitation.