Cryptococcus neoformans infection in an immunocompromised patient is diagnosed by India ink preparation of CSF. The polysaccharide capsule of Cryptococcus primarily evades host immunity by which mechanism?
- A Capsule activates the classical pathway of complement, masking fungal surface
- B Capsule upregulates TLR-4 on macrophages to induce IL-10 production
- C Capsule inhibits phagocytosis by interfering with complement receptor-mediated opsonisation; shed capsular antigen decoys anti-capsular antibodies ✓
- D Capsule triggers robust Th1 CD4+ T cell response clearing the organism
Explanation
The Cryptococcus neoformans polysaccharide capsule (mainly glucuronoxylomannan, GXM) is a major virulence factor with multiple immune evasion mechanisms: (1) it impairs phagocytosis by inhibiting complement receptor 3 (CR3)-mediated opsonophagocytosis; (2) shed GXM acts as a decoy antigen, sequestering anti-capsular antibodies and complement components; (3) GXM inhibits neutrophil and macrophage migration; (4) it interferes with antigen presentation, skewing immunity toward a non-protective Th2 response. Cryptococcal antigen (CrAg) lateral flow assay on CSF/serum is highly sensitive (>99%) and specific for diagnosis. Treatment: liposomal amphotericin B + flucytosine (induction 2 weeks), then fluconazole consolidation/maintenance.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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