Coexpression of hGM (M) Rα and hβ_c in FDCP-mix cells.

(A) Cell surface expression. Cells transfected with hGM (M) Rα in combination with hβ_c cells were analyzed for expression of the extracellular domains of the hGM Rα and hβ_c by flow cytometry. Cells were sequentially incubated with (i) anti-hGM Rα antibody or (ii) anti-hβ_c antibody and FITC-conjugated antimouse secondary antibody. The solid gray histogram represents the cell autofluorescence obtained in the absence of antibody staining. Representative histograms are shown for labeling obtained in the presence of secondary antibody only (gray) and in the presence of both primary and secondary antibody (black). (B) Effects on cell survival. Cells coexpressing hGM (M) Rα, hβ_c (░) were cultured in the presence of hGM-CSF (0-100 ng/mL) for 48 hours prior to assessment of cell viability based on trypan blue exclusion. The data obtained for the chimeric hGM/β_c, hβ_c (▪) are shown for comparison. Results are expressed as a percentage of the rmIL-3 (10 ng/mL) response and are mean values ± SEM of 3 experiments. (C) Long-term proliferation. Cells coexpressing either hGM/β_c, hβ_c (●) or hGM (M) Rα, hβ_c (▴) were cultured for 60 days in the presence of hGM-CSF (1 ng/mL). The growth rate was determined from the initial and subsequent cultures of cells seeded at 1 × 10⁵/mL and resuspended in fresh media when the cell number was more than 5 × 10⁵/mL. The results are expressed as log viable cell number/mL. The growth rates of hGM/β_c, hβ_c() and hGM (M) Rα, hβ_c() cells in response to rmIL-3 (10 ng/mL) are also shown. Results are mean ± SEM of 3 experiments.