Recognizes a single chain glycoprotein of 70kDa, identified as CD55. This MAb was clustered in Kobe at the Sixth International Workshop on Human Leukocyte Differentiation Antigens as F429D-9 (N-L120). CD55/DAF is widely expressed on cells throughout the body including leukocytes, erythrocytes, epithelium, endothelium, and fibroblasts. It is a Glycosyl phosphatidylinositol anchored (GPI-anchored) member of the membrane bound complement regulatory proteins that inhibit autologous complement cascade activation. It prevents the amplification steps of the complement cascade by interfering with the assembly of the C3-convertases, C4b2a and C3bBb, and the C5-convertase, C4b2a3b and C3bBb3b. CD55 also serves as receptor for CD97 and for echovirus and Coxsackie B virus. Anti-CD55 can be used as marker for paroxysmal nocturnal hemoglobinuria (PNH).