Decay-accelerating factor (DAF) may play a role in allergies

Decay accelerating factor (CD55) is a membrane protein that regulates the complement system on the cell surface. CD55 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.


CD55 molecule, decay accelerating factor for complement (Cromer blood group). Image source: Wikipedia, public domain.

DAF is not expressed on RBCs in paroxysmal nocturnal hemoglobinuria (PNH) type III. CD59 absence also leads to PNH. Type I cells have normal levels of CD55 and CD59, type II have reduced levels and type III have absent levels. CD59 is also called membrane inhibitor of reactive lysis (MIRL).

Mnemonic

CD59 blocks
C5-9
components of the complement, MAC, from perforating the cell membrane

In paroxysmal nocturnal hemoglobinuria, patients report episodic dark urine due to hemoglobinuria during intravascular hemolysis, which often occurs at night. Early morning urine is cola-colored. This may occur at different times of the day and vary from patient to patient.

The term "nocturnal" refers to the initial belief that hemolysis is triggered by acidosis during sleep and activates complement to hemolyze an unprotected and abnormal RBC membrane. However, hHemolysis occurs throughout the day and is not actually paroxysmal, but the urine concentrated overnight produces the dramatic change in color.

From Clinical & Experimental Allergy:

Decay-accelerating factor (DAF, CD55) is important for regulation of complement system. The question remains whether it plays a role in allergies.

DAF may be one of the genes involved in conferring susceptibility to allergic respiratory diseases.

In a recent study, decreased levels of DAF were associated with the enhanced specific IgE responses occurring in allergic diseases.

Eculizumab (Soliris) is a humanized mAb against complement protein C5. It is used for treatment of paroxysmal nocturnal hemoglobinuria (PNH).

References:
Paroxysmal Nocturnal Hemoglobinuria: eMedicine Hematology.
The Complement Inhibitor Eculizumab in Paroxysmal Nocturnal Hemoglobinuria. NEJM.
Paroxysmal nocturnal hemoglobinuria. Wikipedia.

Decay-accelerating factor from Roitt's essential immunology By Ivan Maurice Roitt, Peter J. Delves:



Updated: 11/18/2009