An AIDS patient (CD4 = 45/µL) presents with headache, fever and confusion for one week. CSF shows: opening pressure 320 mmH₂O, WBC 5/µL (lymphocytes), protein 60 mg/dL, glucose 35 mg/dL (serum 90 mg/dL), and India ink preparation shows encapsulated yeast. Which virulence factor of Cryptococcus neoformans directly explains the large capsule seen?
- A Melanin produced by laccase enzyme depositing in the cell wall
- B Phospholipase B degrading pulmonary surfactant during initial lung infection
- C Mannoprotein antigens triggering excessive Th2 response in immunocompromised host
- D Polysaccharide capsule composed of glucuronoxylomannan (GXM) that interferes with phagocytosis, complement activation and T-cell proliferation ✓
Explanation
Cryptococcus neoformans has a large polysaccharide capsule (visible as a halo on India ink preparation) primarily composed of glucuronoxylomannan (GXM) and galactoxylomannan (GalXM). The capsule is the primary virulence factor: it inhibits phagocytosis by preventing C3b opsonisation, inhibits neutrophil migration, suppresses T-cell-mediated immunity and impairs dendritic cell antigen presentation. In AIDS, cryptococcal meningitis can present with very high opening pressure (>25 cm H₂O) due to capsular polysaccharide blocking CSF reabsorption at arachnoid granulations. Melanin (laccase-mediated) also contributes to virulence by scavenging free radicals in macrophages.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.