SCF activates hematopoietic cells during acute thrombocytopenia. (A) Quantification of soluble and total SCF in the BM 2 hours after platelet depletion (soluble: Ctrl., n = 10; Depl., n = 12; total: Ctrl., n = 10; Depl., n = 10). (B) Frequency of Mks expressing SCF at the membrane 2 hours after platelet depletion analyzed by flow cytometry (Ctrl., n = 5; Depl., n = 5). (C) Cell cycle analysis of CD41⁻ HSCs and CD41⁻ MPP2 in the absence or presence of c-Kit receptor blocking (ACK2) antibody and/or following platelet depletion (Ctrl., n = 9; Depl., n = 10; Ctrl.+ACK2, n = 4; Depl.+ACK2, n = 5). (D) Phosphorylation of Stat5 and Erk1/2 in control and thrombocytopenic mice, with or without c-Kit receptor blocking 2 hours after platelet depletion (data combined from 2 independent experiments, n = 4). (E) Representative photomicrographs displaying colocalization of CD150⁺/CD48⁻ Lin⁻ HSCs (arrowheads) and Mk (asterisks) 24 hours after platelet depletion. Scale bars represent 15 μm. (F) Frequency of HSCs/Mks relative to the distance between both cell types (2 independent experiments, ≥100 cells per mouse; Ctrl., n = 4; Depl. n = 3). P values were calculated by a 2-tailed unpaired Student t test. (G) Total SCF level in the BM of Pf4-cre⁻; iDTR mice and Pf4-cre⁺; iDTR mice 2 hours after platelet depletion (Ctrl., n = 4; Depl., n = 4). (H) Cell cycle analysis of CD41⁻ HSCs and CD41⁻ MPP2 in Pf4-cre⁻; iDTR mice was performed 12 hours after platelet depletion (Ctrl., n = 8; Depl., n = 13). (I) Cell cycle analysis of CD41⁻ HSCs and CD41⁻ MPP2 in Pf4-cre⁺; iDTR mice was performed 12 hours after platelet depletion (Ctrl., n = 7; Depl., n = 6).