t-PA overexpressed by adenoviral transduction is localized to WP bodies.

HUVECs infected with a t-PA–expressing adenovirus and control cells were processed for immunoelectron microscopy (see “Materials and methods”). t-PA, revealed by anti–t-PA monoclonals followed by gold-labeled antimouse antibodies (10 nm gold particles), was located over WP bodies, identified as electron-dense, elongated, and striated structures (panel A). No t-PA labeling was seen in WP bodies from uninfected cells (panel B). VWF and t-PA were revealed by double-label staining, with 5 nm (arrowheads) and 10 nm gold particles (arrows), respectively (panel C). Both antibodies labeled structures similar to the ones described in panel A, confirming their identity as Weibel-Palade bodies. Original magnification: x54 500 (panels A and B) and x74 000 (panel C).