Elevated IL-6 levels inhibit B lymphopoiesis and increase myelopoiesis in B6.Sle1.Yaa mice. Bone marrow cells from wild-type, B6.Sle1.Yaa, and B6.Sle1.Yaa.IL-6^−/− mice were analyzed by flow cytometry. (A) B lymphocytes and myeloid cells from the bone marrow of each animal strain were detected with anti-CD19 and anti–Mac-1 antibodies. The results are representative of 5 separate animals. The percentage of cells in the quadrants is indicated. Numbers in the top left corner show the percentage of CD19⁺ cells in total bone marrow cells; numbers in the bottom right show Mac-1⁺ cells in total bone marrow cells. (B,C) The cell numbers and percentages of CD19⁺ B lymphocytes and Mac-1⁺ myeloid cells in each animal strain are shown. The data were obtained from 5 mice per group and are shown as an average (mean ± SD). Cell numbers are shown as the number from one femur and one tibia. *P < .001, **P < .05 compared with the wild-type, B6.Sle1.Yaa.IL-6^−/− mice.