Decreased surface expression of the WT G-CSFR in cells coexpressing the WT G-CSFR and the Δ319 mutant G-CSFR. Flow cytometry was used to analyze surface expression of the G-CSFR in BaF3 cells transfected with empty vector (Vector), the Δ319 G-CSFR, the WT G-CSFR (WT), or both receptor forms (WT/Δ319). The cells (5 × 105) were incubated with biotin-conjugated anti–G-CSFR antibody (LMM741-biotin), washed, then incubated with Cy5-conjugated streptavidin, and analyzed on a FACSCalibur (BD Biosciences) with a total of 10 000 gated events analyzed.