Decay accelerating factor

Decay accelerating factor (CD55) is a 70 kDa membrane protein that regulates the complement system on the cell surface. It prevents the assembly of the C3bBb complex (the C3-convertase of the alternative pathway) or accelerates the disassembly of preformed convertase, 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.

Pathology
DAF is not expressed on paroxysmal nocturnal hemoglobinuria III (markedly abnormal) RBCs; however, this deficiency is not the cause of PNH.