The human EGF-TM7 receptor EMR3 is a marker for mature granulocytes

EMR3 is a member of the epidermal growth factor-seven-transmembrane (EGF-TM7) family of adhesion class TM7 receptors. This family also comprises CD97, EMR1, EMR2, and EMR4. To characterize human EMR3 at the protein level, we generated Armenian hamster mAb. Using the mAb 3D7, we here demonstrate that EMR3, like other EGF-TM7 receptors, is expressed at the cell surface as a heterodimeric molecule consisting of a long extracellular alpha-chain, which possesses at its N-terminus EGF-like domains and a membrane-spanning beta-chain. Flow cytometric analysis revealed that all types of myeloid cells express EMR3. In peripheral blood, the highest expression of EMR3 was found on granulocytes. More mature CD16(+) monocytes express high levels of EMR3, and CD16(-) monocytes and myeloid dendritic cells (DC) are EMR3(dim/low). Lymphocytes and plasmacytoid DC are EMR3(-). It is interesting that in contrast with CD97 and EMR2, CD34(+)CD33(-)/CD38(-) committed hematopoietic stem cells and CD34(+)CD33(+)/CD38(+) progenitors in bone marrow do not express EMR3. In vitro differentiation of HL-60 cells and CD34(+) progenitor cells revealed that EMR3 is only up-regulated during late granulopoiesis. These results demonstrate that the expression of EGF-TM7 receptors on myeloid cells is differentially regulated. EMR3 is the first family member found mainly on granulocytes.