Electron microscopic immunolocalization of seminal vesicle-specific antigen in human seminal vesicle

Seminal vesicle-specific antigen (SVSA) has been shown to be a polymorphic antigen represented by multiple immunoreactive peptides when fresh human semen is probed with monoclonal antibody (MHS-5) on Western blots. Semen samples collected directly into sodium dodecyl sulfate (SDS) demonstrate major immunoreactive peptide bands at 69-71 kDa and 58 kDa as well as a series of peptides of lower molecular mass. As semen liquefies, the higher molecular mass forms of SVSA are transformed into lower molecular mass bands, with 10-13 kDa immunoreactive peptides predominating after 8 h of liquefaction (McGee and Herr, Biol. Reprod. 37:431-439, 1987). In the present study, the 10-13 kDa form of SVSA was purified by preparative electrophoresis from SDS gels and a polyclonal antibody was generated in guinea pigs. Human seminal vesicle was fixed by immersion in combinations of glutaraldehyde and paraformaldehyde and embedded in Araldite or LR Gold. Both the guinea pig polyclonal antibody and the murine monoclonal antibody MHS-5 were employed to localize SVSA in human seminal vesicle by immunoelectron microscopy using Protein-A gold complexes. Gold particles were quantified in various subcellular compartments by a Videoplan computer. With either antibody probe, SVSA was found predominantly in the central electron-dense cores of secretory granules, with no staining evident over the electron lucent halo surrounding the granule core. With preimmune serum, the mean number of gold particles overlying secretory granules was 3/microns2; with polyclonal anti-SVSA, the mean number of particles observed over secretory granules was 182/microns2. This study represents, to our knowledge, the first fine-structural localization of a specific secretory protein to the electron-dense cores of secretory granules in principal cells of the human seminal vesicle.