The mechanism by which Cryptococcus neoformans evades host phagocytosis is primarily through:
- A A large polysaccharide capsule (glucuronoxylomannan) that inhibits phagocytosis and complement activation ✓
- B Protease production that digests complement components C3 and C5
- C Melanin production in the capsule that neutralises reactive oxygen species
- D Phase variation switching between yeast and hyphal forms to escape immune detection
Explanation
The polysaccharide capsule of Cryptococcus neoformans (primarily composed of glucuronoxylomannan/GXM) is the major virulence factor and antiphagocytic mechanism. The capsule inhibits complement opsonisation by preventing C3b deposition, reduces antigen presentation, suppresses T cell proliferation and NK cell activity, and promotes release of immunosuppressive cytokines (IL-10). The capsule is the basis for the India ink test (negative staining) and cryptococcal antigen (CrAg) lateral flow assay for diagnosis. Melanin (from laccase enzyme) also contributes to resistance to ROS but is secondary to the capsule in antiphagocytic evasion.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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