In leprosy, the Mitsuda (lepromin) test uses integral lepromin (Dharmendra antigen uses heat-killed lepromin). A positive Mitsuda reaction (late reaction at 3–4 weeks) indicates:
- A Active lepromatous leprosy with high bacterial load and intact humoral immune response
- B Prior sensitization by BCG vaccine or prior natural infection providing cell-mediated immunity against Mycobacterium leprae ✓
- C Current seroconversion with IgM antibodies against phenolic glycolipid-I (PGL-I) of M. leprae
- D Secondary immunodeficiency allowing unrestricted multiplication of M. leprae in macrophages
Explanation
The Mitsuda reaction (late reaction: 3–4 weeks — forms a papule/nodule with granuloma on histology) is a measure of cell-mediated immune (CMI) competence against M. leprae. A positive Mitsuda test indicates ability to mount a delayed-type hypersensitivity (Type IV) granulomatous response, as seen in tuberculoid leprosy and healthy individuals with prior BCG vaccination or subclinical M. leprae exposure. Lepromatous leprosy patients have a negative Mitsuda reaction due to M. leprae-specific T-cell anergy. IgM anti-PGL-I serology is used to monitor bacterial load in lepromatous disease.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.