Dominant-negative SYK inhibits phagocytosis.

(A) Phagocytosis of IgG-sensitized sRBCs by noninfected J774A.1 cells (control), cells infected with recombinant vaccinia virus containing empty vector (pSC65-vector), or cells infected with dominant-negative SYK (pSC65-D/N SYK). The cells were infected with vaccinia viruses or empty vector for 4 hours at 37°C with 5% CO₂, after which they were subjected to IgG-sensitized sRBCs in fresh medium at a target-to-effector ratio equal to 100:1 for 2 hours at 37°C. Nonengulfed sRBCs were lysed by water shock and the cells were fixed and stained with Wright Giemsa staining before the phagocytic index was counted. Columns indicate phagocytic index of J774A.1 (mean ± SD). (B) Western blot analysis shows expression of dominant-negative SYK in J774A.1 cells infected with different recombinant vaccinia viruses: lane 1, no vector; lane 2, empty vector; lane 3, dominant-negative SYK.