Human sperm cells express CD44

Objective: To determine whether CD44 is expressed by human sperm cells. Design: Prospective study. Setting: Assisted conception unit and university research laboratory. Patient(s): Fourteen normal fertile donors. Intervention(s): None. Main Outcome Measure(s): Enzyme-linked immunoassay was used to measure the concentration of CD44 in samples of human sperm cells. Immunocytochemistry using a fluorescent antibody system was used to confirm and localize the expression of CD44 on sperm membranes. Western blotting was used to identify CD44 protein in extracts of lysed sperm cells. Result(s): The presence of CD44 was identified in suspensions of pure sperm cells by ELISA. The mean sperm count was 66 million per milliliter (range, 60 million-75 million per milliliter) and the mean concentration of CD44 was 0.013 ng per 10(6) sperm (range, 0.012 ng-0.015 ng per 106 sperm). Use of a fluorescently labeled antibody to CD44 confirmed the presence of CD44 on sperm membranes. CD44 expression was mostly localized in the acrosome region. Western blotting using a specific monoclonal antibody to CD44 identified a variant of CD44 with an approximate molecular weight of 73 kDa. Conclusion(s): The expression of CD44 on the surface of human sperm membranes was confirmed by three independent methods.