Background：CD55 is a 60-70 kD glycosylphosphatidylinositol （GPI）-anchored single chain glycoprotein also known as decay-accelerating factor （DAF）. It is expressed on hematopoietic cells including erythrocytes and many non-hematopoietic cells. CD55 accelerates the dissociation of the components of the C3-convertases （namely C2a from C4b in the C4bC2a complex, a C3-convertase of the classical pathway, and factor Bb from the C3bBb complex, a C3-convertase of the alternative pathway） to protect cells from inappropriate damage caused by autologous complement. CD55 has been reported to reduce the efficiency of NK cell lysis and induce signal transduction in T cells. CD55 has also been shown to interact with CD97 and bind to Coxsackie and Echovirus.
