Capping of CD34^full and CD34^trunc. U937 cells stably transfected with vector (a through f), CD34^full (g through l), or CD34^trunc (m through r) were stimulated for 30 minutes with anti-CD34 (4A1) (d through f, j through l, p through r) or MOPC21 (control) (a through c, g through i, m through o). After fixation, cells were double-stained with anti-CD34 (green channel: a, d, g, j, m, and p) and phalloidin (red channel: b, e, h, k, n, and q), and analyzed by confocal immunofluorescence microscopy. The right-hand panels show superimposed images of green and red channels. Bars, 5 μm.