Mer is not expressed on the surface of murine B-lineage cells. Bone marrow was harvested from wild-type (Mer^+/+), Mer knockout (Mer^−/−), or Mer_Tg C57Bl/6 mice. (A) The remaining lymphocytes were stained with antibodies that bind to the CD45R (B220), CD43, and CD25 surface receptors to classify B cells into various stages of maturation, as depicted in the diagram. Cells were also stained with anti-mouse Mer antibody to detect surface expression of Mer. The histograms demonstrate that Mer is not expressed on the surface of B cells from wild-type mice at any stage of maturation. B cells from Mer^−/− or Mer_Tg mice were used as negative and positive controls, respectively. Representative data from 4 independent experiments are shown. (B) Representative flow cytometry plots from Mer^+/+ and Mer^−/− bone marrow samples identifying the long-term hematopoietic stem cell (LT-HSC; Lin⁻Sca1⁺ckit⁺CD34⁻Flk2⁻), short-term hematopoietic stem cell (ST-HSC; Lin⁻Sca1⁺ckit⁺CD34⁺Flk2⁻), and multipotent progenitor (MPP; Lin⁻Sca1⁺ckit⁺CD34⁺Flk2⁺) populations. (C) Quantification of the LT-HSC, ST-HSC, and MPP populations from Mer^+/+ and Mer^−/− bone marrow (n = 4). (D) Representative flow cytometry plots identifying the megakaryocyte-erythroid progenitors (MEPs; Lin⁻Sca1⁺ckit⁺CD127⁻CD34⁻CD16/32⁻), granulocyte-macrophage progenitors (GMPs; Lin⁻Sca1⁺ckit⁺CD127⁻CD34⁺CD16/32⁺), and common myeloid progenitors (CMPs; Lin⁻Sca1⁺ckit⁺CD127⁻CD34⁺CD16/32⁻) from Mer^+/+ and Mer^−/− bone marrow. (E) Quantification of the MEP, GMP, and CMP populations from Mer^+/+ and Mer^−/− bone marrow (n = 5). All graphs show the mean ± standard error of the mean (SEM) from at least two independent experiments. *P < .05. NS, not significant.