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Difficulty: MediumImmunologic and Inflammatory Processes

Match each patient's clinical presentation with the precise immunopathologic mechanism responsible for their condition.

  • A 23-year-old man presents with his second episode of systemic meningococcal infection despite appropriate prior antibiotic therapy.Deficient formation of the C5b-9 polymeric complex
  • A 35-year-old woman develops non-pitting, non-pruritic facial edema and severe colicky abdominal pain without urticaria, unresponsive to antihistamines.Unregulated kallikrein activation leading to excessive bradykinin production
  • A 19-year-old woman presents with a photosensitive malar rash, severe arthralgias, and proteinuria; laboratory testing reveals an undetectable CH50.Defective opsonization and clearance of circulating immune complexes
  • A 42-year-old man is admitted with chronic fatigue, episodic morning hematuria, and a newly diagnosed acute portal vein thrombosis.Absence of glycosylphosphatidylinositol-anchored complement inhibitors

Answer

The first clinical vignette matches with deficient C5b-9 formation. The second matches with unregulated kallikrein activation. The third matches with defective opsonization of immune complexes. The fourth matches with absence of GPI-anchored inhibitors.
Each vignette represents a classic presentation of a complement-related immunological defect. The terminal pathway is uniquely required to fight Neisseria. The contact system's dysregulation via C1-INH deficiency causes bradykinin-mediated angioedema. The classical pathway is necessary to clear immune complexes, preventing autoimmunity. Finally, PNH is a disorder of absent complement-regulating surface proteins, leading to complement-mediated intravascular hemolysis and thrombosis.

Step-by-Step Solution

1
Identify the underlying disease for each clinical vignette.
Patient 1 has a terminal complement deficiency. Patient 2 has hereditary angioedema. Patient 3 has early complement deficiency-associated SLE. Patient 4 has paroxysmal nocturnal hemoglobinuria.
Accurate clinical diagnosis is required to link the presentation to the underlying foundational science mechanism.
2
Map each identified disease to its specific immunopathologic mechanism.
Terminal complement deficiency limits MAC (C5b-9) formation. Hereditary angioedema involves C1 inhibitor defect leading to excess bradykinin. Early complement deficiency prevents immune complex clearance. PNH lacks CD55/CD59 GPI anchors.
This establishes the foundational pathophysiology connecting clinical syndromes to immunologic processes.

Key Concept

Immunopathogenesis of complement system defects and regulatory protein deficiencies
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Topics

Immunologic and Inflammatory Processes

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