A patient from Bihar presents with fever, splenomegaly, and pancytopenia. Bone marrow aspirate shows amastigotes within macrophages. The organism evades macrophage killing by inhibiting:
- A Phagolysosome fusion via inhibition of phosphatidylinositol 3-kinase
- B Opsonization by cleaving IgG Fc receptors on macrophages
- C Nitric oxide production by downregulating iNOS expression ✓
- D MHC class I antigen presentation to CD8+ T cells
Correct answer: C. Nitric oxide production by downregulating iNOS expression
Explanation
Leishmania donovani amastigotes survive within macrophage phagolysosomes by inhibiting the protein kinase C pathway and suppressing nitric oxide (NO) production by downregulating inducible nitric oxide synthase (iNOS); NO is the primary macrophage killing mechanism for Leishmania. The organism actually survives phagolysosome fusion (unlike Toxoplasma), not by blocking it. IgG Fc receptor cleavage is not a primary escape mechanism. Leishmania primarily infects macrophages which present via MHC class II.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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