Ku is incorporated in vesicles in treated monocytes. (A) A 25 μg portion of the particulate post-nuclear fraction from resting (t0) or activated (t18) monocytes, treated with proteinase K alone or in the presence of Triton X-100, was analysed by western blotting using the indicated antibodies. (B) Monocytes grown on coverslips in complete medium with M-CSF were treated with or without BFA for 90 min (5 μg/ml). Monocytes were fixed and double stained with Ku80 and Giantin antibodies. Similar double staining was carried out with Ku70 and Giantin antibodies. BFA, brefeldin A; CD, cathepsin D; IL 1β, interleukin 1β; M-CSF, monocyte colony-stimulating factor.