CD109: ProductsCD109 is a GPI-anchored member of the alpha-2-macroglobulin (A2M) and complement family of proteins. CD109 is expressed on activated T cells and platelets, hematopoietic stem cells, megakaryocyte precursors, vascular endothelial cells, basal and myoepithelial cells of secretory glands, and squamous cell carcinoma. Human CD109 is produced as a 170 kDa - 180 kDa glycoprotein that is autocatalytically processed to 150 kDa and 120 kDa forms. CD109 on keratinocytes binds TGF-beta and associates with TGF-beta RI and TGF-beta RII, resulting in inhibition of TGF-beta signaling. Polymorphisms of CD109 include the platelet-specific Gov antigen and the blood group ABH antigens. Alloantibodies directed against these antigens result in unsuccessful platelet transfusions, neonatal alloimmune thrombocytopenia, and posttransfusion purpura.