Cell autonomous effect of TGF-β2 on FLT3L responsiveness. (A) Representative example of sort windows used for the isolation of LSK cells. (B) Tgfb2^+/− and wt littermate LSK cell proliferation in response to FLT3L, the combination of KL/TPO, or IL3. Experiments in culture supported by FLT3L were also performed in the presence or absence of 1 pg/mL TGF-β2 (n = 3; *P ≤ .05 in the absence of TGF-β2). A 100% response is defined as that of wt LSK cells at 50 ng/mL FLT3L or IL-3 in the absence of TGF-β2. (C) Tgfb2^−/− (n = 3), Tgfb2^+/− (n = 5), and wt littermate (n = 4) E16 fetal liver LSK cell proliferation in the presence of 10% serum in response to FLT3L (left; *P < .005) or to KL plus TPO (right; P > .4). A 100% response is defined as that of wt LSK cells at 10 ng/mL FLT3L. (D) C57BL/6 LSK cell proliferation in response to FLT3L (left) or KL and TPO (right) in the presence of 10% serum, with or without SB-431542 (10μM in DMSO; n = 3; *P = .002). (E) Tgfb2^+/− and wt littermate LSK cell proliferation in serum-free cultures in response to FLT3L (n = 3; P > .1). A 100% response is defined as that of wt LSK cells at 50 ng/mL FLT3L. (F) Clone size (left; n = 80 for wt, n = 83 for Tgfb2^+/−; *P = .02 by Student's unpaired t test) and cloning efficiency (right; n = 4; P = .736) of single Tgfb2^+/− or wt LSK cells in liquid cultures containing 50 ng/mL FLT3L and 10% serum. Data collected after 5 days of incubation. Error bars represent SEM.