Complement decay-accelerating factor, also known as CD55 or DAF, is a protein that, in humans, is encoded by the CD55gene.
DAF regulates the complement system on the cell surface. It 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 of the classical and lectin pathways interferes with the conversion of C2 to C2a, thereby preventing formation of the C4b2a C3 convertase, and interaction of DAF with C3b of the alternative pathway interferes with the conversion of factor B to Bb by factor D, thereby preventing formation of the C3bBb C3 convertase of the alternative pathway. Thus, by limiting the amplification convertases of the complement cascade, DAF indirectly blocks 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.
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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^Spiller OB, Goodfellow IG, Evans DJ, Almond JW, Morgan BP (January 2000). "Echoviruses and coxsackie B viruses that use human decay-accelerating factor (DAF) as a receptor do not bind the rodent analogues of DAF". J. Infect. Dis. 181 (1): 340–3. doi:10.1086/315210. PMID10608785.
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