Epididymal Secretion of a Mouse Sperm Surface Component Recognized by a Monoclonal Antibody

We have generated a monoclonal antibody directed against an antigenic determinant appearing on the surface of mouse sperm tails during passage through the epididymis (a determinant that we now term sperm maturation antigen number four [SMA 4]). The present study demonstrates that sperm retained in the ductuli efferentes following ligation do not acquire the antigen, suggesting that its appearance is not due to changes intrinsic to the sperm, but that the epididymal environment is required. To examine the role of the epididymis in the appearance of this antigen, sections of unfixed frozen or fixed, paraffin embedded tissue from different regions of the male reproductive tract have been studied by indirect immunofluorescence. Results indicate that the antigen is a secretory product of the epididymal epithelium, produced in a short segment of the distal caput epididymidis. Ligation experiments show that absence of sperm or testicular fluid from the epididymis does not affect production of this antigen. Examination of prepubertal mice indicates that antigen production is age dependent, production beginning in the epididymis in mice between 2 and 4 weeks of age. Indirect immunofluorescence analysis of sections of a variety of tissues and organs shows that the antigen is restricted to sperm and to epithelial cells of the male reproductive tract. Finally, experiments comparing the antibody-induced agglutinability of sperm from the caput epididymidis to that of sperm from the cauda epididymidis gives further evidence that the antigen resides on the sperm surface.