A 40-year-old man with borderline tuberculoid (BT) leprosy develops painful erythematous skin nodules, neuritis, and fever over 3 days. His reaction is classified as Type 1 (reversal reaction). The immunological basis of this reaction is:
- A Immune complex deposition (Type III hypersensitivity)
- B Sudden upgrading of cell-mediated immunity with Th1 cytokine surge ✓
- C IgE-mediated anaphylactic response to M. leprae antigens
- D Th2 cytokine shift with IL-4 and IL-10 predominance
Correct answer: B. Sudden upgrading of cell-mediated immunity with Th1 cytokine surge
Explanation
Type 1 (reversal) reaction occurs in borderline leprosy (BT, BB, BL) due to sudden upregulation of Th1 cell-mediated immunity with increased IFN-γ, IL-2, and TNF-α. This enhances immunological recognition of M. leprae antigens, causing rapid inflammation in existing lesions and nerves. It does not involve immune complexes (that is Type 2/ENL), and is not IgE-mediated. Treatment requires systemic corticosteroids urgently to prevent permanent nerve damage.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.