Inflammation and Immune Pathology USMLE Step 1 Practice Question
A 3-year-old girl presents with recurrent pyogenic infections and hepatosplenomegaly. Vital signs show HR 110/min, RR 28/min, BP 95/60 mmHg, temperature 37.8°C. Laboratory studies reveal WBC 7,200/μL with normal lymphocyte count. Chest X-ray shows no pneumonia. Her immunologist explains that normal phagocytes efficiently ingest encapsulated bacteria because complement coats the bacterial surface. Which complement component serves as the major opsonin facilitating bacterial phagocytosis?
Answer choices
- AFactor B
- BC9
- CC3bCorrect answer
- DC1q
- EC5b
- FF. Mannose-binding lectin (MBL)
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.