CELL SURFACE BASED INACTIVATORS OF COMPLEMENT
CD59 and CD55 are cell surface molecules anchored by glycosylphosphatidylinositol. These two proteins inactivate any C3 convertase molecules deposited on cell surfaces. Somatic mutation of the enzyme (PIGA: Phosphatidylinositol glican class A), needed to generate phospatidylinositol anchors for cell-surface proteins, including CD55 and CD59, in erythroid precursor, results in a condition called paroxysmal nocturnal hemoglobinuria, which is due to the increased susceptibility of red cells to complement-mediated hemolysis. Isolated CD59 deficiency also results in hemolytic anemia.
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