The RMEPCR1560 (1560) antibody reacts with the endothelial protein C receptor (EPCR or CD201), an ~25 kDa type I transmembrane glycoprotein expressed by endothelial cells, subsets of hematopoietic stem cells (HSCs) and dendritic cells, and several malignant cell lines. It is also found in a soluble form in plasma. EPCR exhibits homology with the MHC class 1/CD1 protein family. EPCR binds protein C and activated protein C, thus augmenting protein C activation by the thrombin-thrombomodulin complex and regulating blood coagulation and inflammation. EPCR protein expression has been detected on ~1.5% of mouse bone marrow cells. Purified EPCR+ cells are highly enriched for HSC activity, as evidenced by high in vivo repopulation activity. Moreover, EPCR expression is associated with the stem cell activity of bone marrow cell populations isolated using conventional markers, indicating the usefulness of EPCR as a single marker for the identification of mouse HSCs.