Polymorphous light eruption (PMLE) is the most common photodermatosis. Which of the following correctly describes its immunopathogenesis?
- A IgE-mediated immediate hypersensitivity to UVA photoproducts
- B Failure of UV-induced immunosuppression allowing delayed-type hypersensitivity to cutaneous photoantigen ✓
- C Complement-mediated cytotoxic reaction to porphyrin photoactivation
- D Type I photosensitivity reaction mediated by reactive oxygen species alone
Correct answer: B. Failure of UV-induced immunosuppression allowing delayed-type hypersensitivity to cutaneous photoantigen
Explanation
PMLE is thought to result from a failure of the normal UV-induced immunosuppression (Treg activation, urocanic acid isomerisation to cis-UCA). This allows a delayed-type hypersensitivity (DTH/Type IV) reaction against UV-modified cutaneous photoantigens to proceed, manifesting as the characteristic pruritic polymorphous eruption (papules, vesicles, plaques) hours to days after sun exposure. It is NOT IgE-mediated. Treatment includes hardening (graduated sunlight exposure), NB-UVB, and antimalarials.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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