Complement System

A 32-year-old woman with recurrent Neisseria meningitidis infections is found to have a deficiency in the terminal complement components. Which is the most common terminal complement component deficiency predisposing to meningococcal disease?

A 28-year-old woman from Delhi presents with recurrent episodes of angioedema affecting her face, lips, and throat over the past 6 months. She denies urticaria. On examination, she is afebrile with normal vital signs. Serum C1 esterase inhibitor (C1-INH) level is 15% (normal 50–150%), and C1q level is normal. What is the most appropriate next step in management?

A 35-year-old man from Bangalore with a history of recurrent Neisseria meningitidis infections (2 episodes in the past 18 months) presents to the clinic for evaluation. Serum complement levels show: C5 = 2% (normal 10–20%), C6 = 8% (normal 10–20%), C7 = 12% (normal 10–20%), C8 = 5% (normal 10–20%), C9 = 15% (normal 10–20%). What is the most appropriate next step in management?

Regarding the complement system and its activation pathways, all of the following statements are correct EXCEPT:

Which feature best distinguishes classical complement pathway activation from alternative pathway activation?