A 35-year-old HIV patient (CD4+ count 45 cells/μL) develops progressive confusion, headache, and fever. CSF analysis shows India ink positive encapsulated yeast, elevated CSF opening pressure, low glucose, and minimal pleocytosis. Which virulence factor of Cryptococcus neoformans directly inhibits phagocytosis and prevents complement opsonization?
- A Laccase enzyme producing melanin in the cell wall
- B Phospholipase B promoting cell membrane invasion
- C Urease activity causing tissue damage
- D Polysaccharide capsule (composed of glucuronoxylomannan — GXM) ✓
Explanation
The polysaccharide capsule of Cryptococcus neoformans (composed predominantly of glucuronoxylomannan, GXM) is its primary virulence factor, directly inhibiting phagocytosis by macrophages and neutrophils. The capsule also: shed GXM moieties block complement deposition and opsonization, scavenges reactive nitrogen species, inhibits leukocyte migration, and suppresses T-cell activation (reducing IFN-γ and IL-12 production). Melanin (from laccase) protects against antifungal drugs and oxidative killing. The cryptococcal capsular antigen (CrAg lateral flow assay) in CSF/serum is >99% sensitive for diagnosis. Treatment: liposomal amphotericin B + flucytosine induction, then fluconazole maintenance.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.