DAFCD55

DAFCD55 is an alternative designation for the protein known as CD55, or decay-accelerating factor (DAF). It is a cell-surface glycoprotein that plays a key role in regulating the complement system, helping to protect host cells from unintended complement-mediated damage.

CD55 is a glycosylphosphatidylinositol (GPI)-anchored protein, meaning it attaches to the outer leaflet of the cell membrane without spanning the membrane. It is broadly expressed on many cell types, with high levels on endothelial and blood cells. By accelerating the decay of C3 and C5 convertases in both the classical and alternative complement pathways, CD55 dampens the amplification of the complement cascade and reduces the formation of membrane attack complexes.

The CD55 gene encodes the CD55 protein in humans. In addition to its regulatory function, CD55 can serve as a receptor for certain pathogens, including some echoviruses and coxsackieviruses, facilitating viral entry in susceptible cells.

Clinical relevance of CD55 includes its role in paroxysmal nocturnal hemoglobinuria (PNH). PNH commonly results from a deficiency in glycosylphosphatidylinositol anchors, leading to loss of CD55 (and CD59) from blood cells and increased sensitivity to complement-mediated lysis. CD55 expression is also used as a diagnostic marker in flow cytometry to profile blood cells, and therapeutic approaches that modulate complement activity—such as inhibitors targeting downstream components—address diseases where CD55 regulation is disrupted.

In research and clinical contexts, DAFCD55 is generally treated as synonymous with CD55, the decay-accelerating factor, a crucial regulator of the complement system on host cell surfaces.