CHE and Alk enhance Fc-mediated phagocytosis by a Syk-dependent mechanism. PMNs were isolated an incubated in the presence (+) or absence (−) of GM-CSF, CHE, Alk or Syk II inhibitor (SykII). Phagocytosis of opsonized SRBCs (A) or Syk activation (B) were determined as described in Methods. A, results are means ± SEM (n = 4). *, p < 0.05 vs Ctrl (GM-CSF, CHE, Alk or SykII) and #, p < 0.05 vs GM-CSF for the indicated columns. B, upper panel is the phosphorylated form of Syk, whereas the bottom panel illustrated the non-phosphorylated form of Syk, following stripping indicating equal protein loading. Results are from one representative experiment out of three.