One form of anemia results when individuals have a deficiency in the enzyme phosphatidylinositol glycan A (PIGA). This enzyme is required for the membrane attachment of proteins anchored by glycolipids to the plasma membrane, using what is called a 'GPI-linkage.' Included in the group of GPI-linked cell surface proteins is DAF/CD55. These individuals become anemic because:
A) DAF/CD55 prevents the lysis of red blood cells by infecting pathogens.
B) DAF/CD55 normally prevents the spleen from clearing healthy red blood cells from the circulation.
C) In the absence of PIGA, the red blood cell membrane is bare of proteins allowing increased access of complement activating proteins to attach to the cell membrane.
D) DAF/CD55 is a complement inhibitory protein that inactivates any C3 convertase that may form on host cell surfaces.
E) In the absence of PIGA, red blood cells are unable to synthesize high levels of hemoglobin.

Question

Quizplus · Accepted Answer

DAF/CD55 is a complement inhibitory protein that prevents the formation of C3 convertase on host cell surfaces, thereby protecting cells from being lysed by the complement system. In the absence of PIGA, GPI-linked proteins like DAF/CD55 cannot anchor to the cell membrane, leaving red blood cells vulnerable to complement-mediated lysis.

One Form of Anemia Results When Individuals Have a Deficiency