Effects of the soluble receptor on apoptosis. CD34⁺ cells from 1 PMF patient (m2) were cultured without growth factor in the absence (A, C, and E) or the presence of the sMpl-Fc (B, D, and F). At day 4 of culture, cells were labeled by an APC-conjugated anti-CD34 MoAb and a R-PE–conjugated anti-CD41a MoAb. They were subsequently stained by Annexin-FITC and 7AAD. CD34⁺CD41⁻ (R1) and CD34⁺CD41⁺ (R2) were gated only on the fluorescence labeling without taking into account their scatter properties. 7AAD and Annexin binding was studied in the gate R1 (C and D) and in the gate R2 (E and F). Early and late apoptosis correspond to the low right quadrant (AnnexinV⁺7AAD⁻) and the up right quadrant (AnnexinV⁺7AAD⁺), respectively. Similar results were obtained with cells of two other patients.