Overexpression of SHP-1 in J774A.1 cells inhibits phagocytosis.

(A) Composite photomicrographs of Wright Giemsa–stained J774 cells undergoing phagocytosis of sRBCs. Original magnification, × 100. We show noninfected J774 A.1 cells (control); cells infected with recombinant vaccinia virus containing empty vector (pSC65-vector); J774 cells infected with recombinant vaccinia virus encoding wild-type SHP-1 (pSC65-SHP-1); cells containing catalytically dead SHP-1 mutant (pSC65-C2). The cells were infected with vaccinia viruses or empty vectorfor 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. (B) Quantitation of phagocytosis of IgG-sensitized sRBCs by J774A.1 cells. Columns indicate phagocytic index of J774A.1 cells (mean ± SD). (C) Western blot analysis shows expression of SHP-1 protein in J774A.1 cells infected with recombinant vaccinia virus: lane 1, no vector; lane 2, empty vector; lane 3, catalytically dead C2-SHP-1 mutant; lane 4, wild-type SHP-1 .