In paroxysmal nocturnal hemoglobinuria (PNH), the deficiency of GPI-anchored proteins CD55 and CD59 leads to complement-mediated hemolysis. Eculizumab targets which complement component?
- A C5 (prevents cleavage into C5a and C5b) ✓
- B C3 convertase
- C C1q (classical pathway initiation)
- D Factor D of the alternative pathway
Explanation
Eculizumab is a monoclonal antibody against C5 that prevents its cleavage into C5a (an anaphylatoxin) and C5b (which initiates membrane attack complex formation). By blocking C5 cleavage, eculizumab halts the terminal complement cascade and prevents intravascular hemolysis in PNH. CD59 normally prevents MAC (C5b-9) assembly; CD55 normally accelerates decay of C3/C5 convertases. In PNH, loss of these GPI-anchored regulators leaves erythrocytes vulnerable to complement. Ravulizumab (long-acting anti-C5) and iptacopan (anti-Factor B, proximal complement inhibition) are newer options.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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