The blood-epididymis barrier and human male fertility.

Spermatozoa undergo a posttesticular maturation in the epididymis to acquire motility and the capacity to fertilize. Sperm maturation depends in part upon the creation of a specific microenvironment within the epididymal lumen. This environment is conditioned by proteins secreted by the epithelium and by exchange of molecules between the lumen and the blood circulation. These exchanges are selectively regulated by the blood-epididymis barrier. The blood-epididymis barrier is comprised of apical tight junctions between adjacent principal cells. Adherens junctions, which are necessary for cell adhesion, can also be found at the junctional complex present between adjacent principal cells. Progress has been made on the understanding of cellular interactions in the epididymis as well as the regulation of the luminal microenvironment and its importance for sperm maturation in rodents and humans. Clearly, changes in the function of cellular junctions in the human epididymis are associated with male infertility.