False statement about DAF VecoM A ccelerating Facton A) Prevents formation of C3 convertase 21% B) Inhibit formation of MAC 38% C) Also known as CD55 16% D) Linked to plasma membrane by GPI anchor
Reading File
Finding Sources
Reading File
The answer is B) Inhibit formation of MAC.
Explanation
DAF (Decay Accelerating Factor) facts:
| Feature | Correct Statement |
|---|---|
| Also known as | CD55 ✅ |
| Membrane attachment | GPI anchor (glycophosphatidylinositol) ✅ |
| Function | Prevents formation/accelerates decay of C3 convertases (both classical C4b2a and alternative C3bBb) ✅ |
| Inhibits MAC? | NO ❌ — this is the function of CD59 (protectin/MIRL) |
From Robbins & Kumar Basic Pathology:
"Decay accelerating factor (DAF) and CD59 are two proteins that are linked to plasma membranes by a GPI anchor. DAF prevents formation of C3 convertases and CD59 inhibits formation of the membrane attack complex."
So option B is FALSE — DAF does not inhibit MAC formation. It is CD59 that inhibits MAC.
This is clinically relevant in Paroxysmal Nocturnal Hemoglobinuria (PNH), where a somatic mutation in the PIG-A gene disrupts GPI anchor synthesis, causing loss of both DAF (CD55) and CD59. The resulting uncontrolled complement activation leads to intravascular hemolysis.
Which of the following statements are true about Factor H A) Inhibits alternative pathway of complement activation B) Inherited defects in Factor H can cause an atypical form of HUS C) Polymorphisms in Factor H gene have been linked to ARMD D) All of the above
Finding Sources
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Reading File
The answer is D) All of the above — all three statements about Factor H are true.
Factor H — Key Facts
A) Inhibits the alternative pathway of complement activation ✅
Factor H is a soluble plasma glycoprotein that regulates the alternative pathway by:
- Binding to C3b and accelerating the decay of the alternative C3 convertase (C3bBb)
- Acting as a cofactor for Factor I to proteolytically cleave C3b
Its deficiency leads to uncontrolled C3 consumption and excessive complement activation. — Robbins & Kumar Basic Pathology
B) Inherited defects in Factor H can cause an atypical form of HUS ✅
Mutations in the CFH gene (complement factor H gene) cause atypical HUS (aHUS) — a thrombotic microangiopathy driven by uncontrolled alternative pathway activation on endothelial surfaces (as opposed to typical/STEC-associated HUS which is toxin-mediated).
"Mutations in Factor H are associated with a kidney disease called the hemolytic uremic syndrome." — Robbins & Kumar Basic Pathology
C) Polymorphisms in the Factor H gene are linked to Age-Related Macular Degeneration (ARMD) ✅
The Y402H polymorphism in the CFH gene is one of the strongest known genetic risk factors for age-related macular degeneration (wet/AMD). Dysregulated complement activation in the choroid/retinal vasculature drives the drusen deposits and neovascularization characteristic of wet ARMD.
"Mutations in Factor H are associated with... wet macular degeneration of the eye, characterized by increased permeability of retinal vessels." — Robbins & Kumar Basic Pathology
Summary Table
| Statement | Verdict |
|---|---|
| Inhibits alternative pathway | ✅ True |
| Inherited defects → atypical HUS | ✅ True |
| Gene polymorphisms → ARMD | ✅ True |
| All of the above | ✅ Correct answer |
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