A patient with borderline tuberculoid (BT) leprosy has a single hypopigmented macule with partial sensory loss. Slit-skin smear (SSS) bacteriological index (BI) is 0. Which immunological test, if performed, would show the strongest delayed-type hypersensitivity reaction?
- A ELISA for anti-PGL-1 IgM antibodies
- B Lepromin (Mitsuda) test ✓
- C Complement fixation test for M. leprae antibodies
- D Lymphocyte transformation test to M. leprae antigens
Correct answer: B. Lepromin (Mitsuda) test
Explanation
The lepromin (Mitsuda) test measures delayed-type hypersensitivity to autoclaved M. leprae and is read at 28–30 days (Mitsuda reaction, nodule ≥5 mm = positive). BT leprosy, being at the tuberculoid end of the immunological spectrum with high cell-mediated immunity, gives a strongly positive Mitsuda reaction. Anti-PGL-1 IgM (detected by ELISA) is elevated in lepromatous pole where bacillary load is high (high BI), not in paucibacillary disease. Lepromin is not a diagnostic test but an immunological marker of host resistance.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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