(A) Inhibition of antibody-induced cap formation. (A) Distribution of CD34 or CD43 on KG1a cells stimulated for 30 minutes with anti-CD34 (4A1, a through l) or anti-CD43 (MEM59, m through x) in the presence of medium alone (a through d, m through p), Cyt.D (e through h, q through t), or NaF (i through l, u through x) as described in Materials and Methods. After fixation, cells were double-stained either with anti-CD34 (green channel: b, f, and j) and phalloidin (red channel: c, g, and k) or with anti-CD43 (green channel: n, r, and v) and phalloidin (red channel: o, s, and w), and then analyzed by Nomarski differential-interference-contrast (left-hand panels) and confocal immunofluorescence microscopy. The right-hand panels show superimposed images of green and red channels. Bars, 10 μm. (B) Anti-pTyr Western blot of equal amounts of Triton X-100 lysates from KG1a cells stimulated with anti-CD34 (lanes 1 through 3) or anti-CD43 (lanes 4 through 6) in the presence of medium alone (lanes 1 and 4), 10 μg/mL cytochalasin D (Cyt.D) (lanes 2 and 5), or 30 mmol/L NaF (lanes 3 and 6) as described above. Molecular size markers are indicated on the left (kD). (C) Homotypic cytoadhesion of KG1a cells stimulated for 90 minutes with anti-CD34 (a through c), anti-CD43 (d through f), or control antibody (g through i) in the presence of medium alone (a, d, and g), 10 μg/mL Cyt.D (b, e, and h), or 30 mmol/L NaF (c, f, and i). Bars, 80 μm.