Endothelial Kitl deletion results in reduced HSC numbers and reduced systemic levels of sKITL. (A) Mean (± standard error of mean [SEM]) total BM mononuclear cells from 2 femurs and 2 tibias of 4-week-old Sl/+ (n = 3) and Sl/Tie2Δ (n = 5) mice. (B-C) Representative fluorescence-activated cell sorter (FACS) profiles with gated cell populations as percentages of total BM cells (B) and mean (± SEM) Lineage^–Sca1⁺KIT⁺ (LSK) CD150⁺CD48^– HSC numbers (C) of 4-week-old Sl/+ (n = 3) and Sl/Tie2Δ (n = 5) mice. (D) Mean (± SEM) percent donor (CD45.2) contribution in total PB toward total white blood cells (WBCs), MAC1⁺GR1⁺ myeloid cells, CD19⁺ B cells, and CD4/CD8a⁺ T cells 6 and 16 weeks after competitive transplantation of Sl/+ (n = 3 donors) or Sl/Tie2Δ (5 donors) BM cells. (E) Mean (± SEM) numbers of pre–megakaryocyte-erythroid (preMegE), megakaryocyte (MkP), colony forming unit–erythroid (CFU-E), pre–granulocute-monocyte (preGM), and granulocyte-monocyte (GMP) progenitor cells from 2 femurs and 2 tibias of 4-week-old Sl/+ (n = 3) and Sl/Tie2Δ (n = 5) mice. (F) Mean (± SEM) blood serum sKITL levels determined by enzyme-linked immunosorbent assay (ELISA) from 4-week-old Sl/+ (n = 4) and Sl/Tie2Δ (n = 5) mice. (G-H) Mean (± SEM) total BM mononuclear cell (G) and LSK CD150⁺CD48^– HSC (H) numbers from 2 femurs and 2 tibias of 3-week-old ΔEx7 and wild-type littermate controls (n = 5 per genotype). (I) Mean (± SEM) committed myelo-erythroid progenitor cell numbers from 2 femurs and 2 tibias of 3-week-old ΔEx7 and wild-type littermate controls (n = 4-5 per genotype). All data represent mean ± SEM, and the nonparametric Mann-Whitney test was used to assess statistical significance. ∗P < .05; ∗∗P < .01.