Decay-accelerating factor

Complement decay-accelerating factor, also known as CD55 or DAF, is a is_associated_with::protein that, in humans, is encoded by the CD55 is_associated_with::gene.

Decay accelerating factor is a 70 kDa is_associated_with::membrane protein that regulates the is_associated_with::complement system on the cell surface. DAF recognizes C4b and C3b fragments that are created during C4 (is_associated_with::classical complement pathway and is_associated_with::lectin pathway) and C3 (is_associated_with::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 is_associated_with::membrane attack complex.

This is_associated_with::glycoprotein is broadly distributed among is_associated_with::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 is_associated_with::paroxysmal nocturnal hemoglobinuria; in that disorder, red blood cells with very low levels of DAF and is_associated_with::CD59 undergo complement-mediated hemolysis.

Infectious diseases
DAF is used as a receptor by some is_associated_with::coxsackieviruses and other is_associated_with::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.