Type 2 lepra reaction (Erythema Nodosum Leprosum, ENL) is characterised by which immunological mechanism?
- A Type IV (delayed-type) hypersensitivity — reversal reaction
- B Type III (immune complex-mediated) hypersensitivity — Arthus reaction ✓
- C Type I (IgE-mediated) anaphylactic hypersensitivity
- D Type II (antibody-dependent cytotoxic) hypersensitivity
Correct answer: B. Type III (immune complex-mediated) hypersensitivity — Arthus reaction
Explanation
ENL is a Type III immune complex-mediated reaction occurring in lepromatous (LL) and borderline lepromatous (BL) patients. Massive antigen load from dead bacilli forms immune complexes that deposit in tissues and activate complement, causing systemic inflammatory symptoms, tender erythematous nodules, fever, arthralgia, neuritis, orchitis, and iritis. Reversal reaction (Type 1) is Type IV DTH. ENL is treated with thalidomide (males) or high-dose prednisolone.
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.