Sperm selection capacity of the human zona pellucida

Abstract

Previous hemizona assay (HZA) results have illustrated a positive and significant correlation between the percentage of morphologically normal spermatozoa in the semen and the number of spermatozoa tightly bound to the zona pellucida. The present study was designed to evaluate the morphologic features using strict criteria of spermatozoa tightly bound to the zona pellucida. Semen samples of 4 normozoospermic and 11 teratozo‐ospermic men were used to compare the percentage of normal spermatozoa in the semen with that found (1) after swim‐up separation and (2) bound to the zona under HZA conditions. The mean (± SEM) % normal forms for normozoospermic men in semen, after swim‐up and zona‐bound spermatozoa were 21.5 ± 1.6, 27.5 ± 2.9, and 44.8 ± 3.4, respectively. A significantly higher % of normal forms were found among zona‐bound sperm compared to swim‐up forms (p = 0.02) and seminal sperm (p = 0.02). The mean % of normal sperm forms present in semen, after swim‐up and zona pellucida‐binding for teratozoospermic men, were 3.7 ± 0.9, 5.8 ± 1.6 and 15.6 ± 3.1, respectively. Significant differences existed between the % of normal sperm forms found in the swim‐up and zona‐bound spermatozoa (P = P = <0.0003, respectively) compared to the original ejaculates. Results indicate that a selective process against abnormal spermatozoa occurs at the site of the zona pellucida. Spermatozoa classified as normal or slightly abnormal are selectively bound to the zona in favor of abnormal (bizarre) spermatozoa; particularly those sperm cells with acrosomal abnormalities are either actively excluded or simply cannot bind to the zona or do it with a low efficiency due to inherent defects. This newly identified human zona property of sperm selectivity points out another potential use of the HZA, i.e., selection of sperm to be used in assisted fertilization.