In leprosy, the Mitsuda (lepromin) reaction is read at 4 weeks and represents a granulomatous response to M. leprae antigens. A positive Mitsuda reaction indicates:
- A Good cell-mediated immunity against M. leprae — associated with tuberculoid and borderline tuberculoid spectrum ✓
- B Active leprosy infection — lepromin is a diagnostic test for current disease
- C Past or current M. leprae infection (equivalent to Mantoux for tuberculosis)
- D Humoral immunity with high anti-PGL-1 antibody levels
Explanation
The Mitsuda (late lepromin) reaction at 28 days (4 weeks) reflects the degree of cell-mediated immunity (CMI) against M. leprae. A positive reaction (>5 mm indurated nodule) indicates intact CMI and is associated with tuberculoid leprosy (TT) and borderline tuberculoid (BT), where T helper 1 responses control bacillary multiplication. It is not a diagnostic test — lepromatous patients (with absent CMI) are Mitsuda-negative. Persons without leprosy exposure can also be Mitsuda-positive. The early Fernandez reaction (48 hours) is similar to tuberculin-type DTH and tests shared antigens; anti-PGL-1 IgM indicates bacterial load.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.