This antibody reacts with an extracellular epitope of CD105, a 90 kDa type I homodimerizing membrane glycoprotein expressed on vascular endothelial cells (small and large vessels), activated monocytes and tissue macrophages, stromal cells of certain tissues including bone marrow, pre-B lymphocytes in fetal marrow, and erythroid precursors in fetal and adult bone marrow. It is also present on syncytiotrophoblast on placenta throughout pregnancy.