A patient with borderline tuberculoid leprosy develops a sudden, painful, erythematous swelling of existing skin lesions along with fever and nerve tenderness. This is classified as a Type 1 lepra reaction. Which immunological mechanism underlies this?
- A Immune complex deposition causing complement activation
- B Upgrading or downgrading of cell-mediated immunity with Th1 shift ✓
- C IgE-mediated mast cell degranulation
- D Antibody-dependent cellular cytotoxicity
Correct answer: B. Upgrading or downgrading of cell-mediated immunity with Th1 shift
Explanation
Type 1 (reversal) reaction is a delayed hypersensitivity (Type IV) reaction affecting borderline leprosy (BT, BB, BL). It reflects an abrupt shift in immune reactivity — upgrading toward tuberculoid pole or downgrading toward lepromatous pole. Histologically, there is increased granuloma formation with lymphocytic infiltration. The treatment is prednisolone 40–60 mg/day. Type 2 (ENL) is an immune-complex–mediated reaction seen in BL/LL leprosy.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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