Proliferation assay in response to hIL-3 on FDC-P1 cells expressing either IL-3Rα + hβc (A) or IL-3RΔNT + hβc (B) with (□) and without (○) a fixed concentration of MoAb 7G3, showing that this MoAb is able to neutralize IL-3–dependent proliferation from the wild-type receptor (A), but has no effect on IL-3–dependent proliferation from the truncated receptor at the concentration tested (B). Data are the mean of triplicate points ± SD.