Ectopic expression of nonsheddable CD43/34 chimeras is toxic. (A) Flow cytometric analysis of CD43 cell surface expression on CD43-deficient bone marrow cells infected with wt CD43 or CD43/34 chimeras MP and TM. After retroviral infection, cells were differentiated for 5 days into granulocytes and then stimulated for 3 hours with 10 nM TPA (solid line) or vehicle alone (dashed line). Cells shown were gated on GR-1⁺, and data are representative of 3 repeat experiments. (B) Cell yield of CD43-deficient bone marrow cells infected with wt CD43 or CD43/34 chimeras maintained for up to 8 days in IL-3/G-CSF. Numbers of PI⁻ cells are shown for days 0, 2, 4, and 8. n = 4; *P = .001 and **P = .001 (Student t test). (C) Cell yield of CD43-deficient bone marrow cells infected with wt CD43 or CD43/34 chimeras maintained in SCF/M-CSF (top panel) or in IL-3/G-CSF (bottom panel). Percentages of GFP⁺/PI⁻ cells are shown for days 2, 4, and 8 after infection. *P = .01 and **P = .007 (Student t test). (D) Percentage of annexin V⁺/PI⁺ cells is shown at day 8 of CD43-deficient bone marrow cells infected with either wt CD43 or CD43/34 chimeras. During retroviral infection, cells were maintained for 2 days in SCF/Flt3/IL-6, then split and cultured for additional 6 days in either SCF/M-CSF or IL-3/G-CSF. n = 4; *P = .007 and **P = .001 (Student t test). Data are mean ± SD and are representative of at least 3 independent experiments.