Complement decay-accelerating factor, also known as CD55 or DAF, is a protein that, in humans, is encoded by the CD55 gene.
Decay accelerating factor is a 70 kDa membrane protein that regulates the complement system on the cell surface. DAF recognizes C4b and C3b fragments that are created during C4 (classical complement pathway and lectin pathway) and C3 (alternate complement pathway) activation. Interaction of DAF with cell-associated C4b and
C3b proteins interferes with their ability to catalyze the conversion of C2 and factor B to active
C2b (historically called C2a) and Bb and thereby prevents the formation of C4b2b and C3bBb, the amplification convertases of the complement
cascade - thus blocking the formation of the membrane attack complex.
This glycoprotein is broadly distributed among hematopoietic and non-hematopoietic cells. It is a determinant for the Cromer blood group system.
Paroxysmal nocturnal hemoglobinuria
Because DAF is a GPI-anchored protein, its expression is reduced in persons with mutations that reduce GPI levels such as those with paroxysmal nocturnal hemoglobinuria; in that disorder, red blood cells with very low levels of DAF and CD59 undergo complement-mediated hemolysis.
DAF is used as a receptor by some coxsackieviruses and other enteroviruses. Recombinant soluble DAF-Fc has been tested in mice as an anti-enterovirus therapy for heart damage; however, the human enterovirus that was tested binds much more strongly to human DAF than to mouse or rat DAF. Echoviruses and coxsackie B viruses that use human decay-accelerating factor (DAF) as a receptor do not bind the rodent analogues of DAF. and DAF-Fc has yet to be tested in humans.
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- ^ http://www.genecards.org/cgi-bin/carddisp.pl?gene=CD55#function.
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