Identification of dipeptidyl peptidase IV as the antigen of a monoclonal anti-prostasome antibody

BACKGROUND. Our purpose was to elucidate the identity of an antigen of a mo noclonal antibody against prostasomes, which are prostate-derived organelle s occurring freely in human semen. METHODS. Monoclonal antibodies against prostasomes were generated by intras plenic immunization to allow better characterization of the prostasomes. On e third of the resulting antibodies bound to a 110-kDa prostasomal protein on Western blots. RESULTS. The antigen was purified from seminal prostasomes by anion exchang e chromatography and gel electrophoresis. After in-gel digestion and amino- acid sequence analysis of selected peptides, it was identified as dipeptidy l peptidase TV (DPP IV), EC 3.4.14.5, also known as T-cell-activating antig en CD26. No DPP IV could be detected in the supernatant obtained after prep arative ultracentrifugation of the prostasomes. CONCLUSIONS. DPP IV/CD26 is structurally bound to prostasomes rather than b eing free in seminal fluid. This enzyme may play a critical role in the pro moting effect of prostasomes on forward motility of spermatozoa. (C) 1999 W iley-Liss, Inc.