The LSK fraction expresses IL-6 receptor and responds to IL-6 by phosphorylation of STAT-3. (A) Sorted LSK fraction from wild-type bone marrow cells was stained with anti–IL-6Rα or isotype control antibody. LT-HSC and MPP populations were resolved by expression level of Flt3. Stained cells were analyzed by flow cytometry. The results are representative of 3 separate experiments. Splenocyte cells were used as a positive control for IL-6Rα staining (C). (B) The sorted LSK fraction from wild-type bone marrow cells were left unstimulated (NS) or were stimulated with IL-6 (100 ng/mL) for 15 minutes (+IL-6). The cells were fixed, permeabilized, and stained with anti–phospho-STAT3. Stained cells were analyzed by flow cytometry. The results are representative of 3 separate experiments. Splenocyte cells were used as a positive control for phospho-STAT3 staining (D).