Distribution of a proteinase inhibitor of epididymal origin in the tissues and secretions of the male reproductive tract of mice.

Monoclonal antibodies to a low molecular weight, acid-stable acrosin-trypsin inhibitor isolated from epididymal homogenates were used to localize the inhibitor in tissues and secretions of the male reproductive tract of mice. The inhibitor, identified by indirect immunofluorescence, is present in the testes and in the apical portion of the epithelial cells from the caput region of the epididymis of both intact and efferentiectomized animals. Sperm isolated from the testes and caput epididymal region show inhibitor-positive fluorescence on the anterior acrosomal region. The inhibitor could not be localized on ductus or electroejaculated sperm or ductus sperm previously incubated in a purified inhibitor solution. Furthermore, the inhibitor was not visible in the copulatory plug of recently inseminated animals or on sperm recovered from the uterus or from an artificial capacitating medium. The inhibitor could be detected by an enzyme-linked immunosorbent assay in the supernatants of detergent treated or frozen-thawed caput sperm but not of ductus sperm. The data suggest that the inhibitor, made in both the testes and caput epididymis where it associates with the sperm, is lost from the sperm or irreversibly masked during the epididymal sojourn.