Figure 3. Osteolectin⁺ peri-arteriolar stromal cells maintain early lymphoid progenitors by synthesizing SCF.

Images are representative of 3 independent experiments. The same differences that were evident among the frequencies of cell populations were also evident in absolute numbers. (a, b) In femur bone marrow from 2-month-old Scf^GFP/+; Oln^mT/+ mice, Scf-GFP was expressed by both Oln-mTomato⁺ peri-arteriolar cells (arrowhead in a) and Oln-mTomato⁻ peri-sinusoidal cells (arrow in a; scale bar = 20μm). (c-d) Oln^iCreER/+; Scf^fl/fl and Scf^fl/fl littermate control mice were treated with tamoxifen at 2-months of age then bone marrow and spleen cellularity (c), and hematopoietic stem and progenitor cell frequencies in the bone marrow (d) were analyzed one month later (3 independent experiments). (e, f) Localization of IL7Rα⁺Lineage⁻ lymphoid progenitors (arrows) adjacent to peri-arteriolar Osteolectin⁺ cells (scale bar = 15μm; 9 mice in 3 independent experiments). (g) Localization of IL7Rα⁺Lineage⁻ cells in the bone marrow of Oln^iCreER/+; Scf^fl/fl and Scf^fl/fl littermate control mice (6 mice per genotype in 3 independent experiments). (h-j) Oln^iCreER/+; Scf^fl/fl mice and littermate controls were fed tamoxifen from 2–4 months of age and the bone marrow (h) and thymus (i, j) were analyzed (3 independent experiments). (k and l) Compared to Scf^fl/fl controls, Oln^iCreER/+; Scf^fl/fl mice had decreased CLP frequency in the bone marrow (k) and worse survival (l) after Listeria infection (17–27 mice per genotype in 3 independent experiments). All data represent mean ± SD. Statistical significance was assessed using matched samples two-way ANOVAs followed by Sidak’s multiple comparisons tests (c, d, h-k), Cochran-Mantel-Haenszel tests (f, g), or Mantel-Cox test (l).