Sequential histological study of lepromin reaction.

Skin testing with Dharmendra antigen was performed on 55 patients with TT, BT, BL, and LL types of leprosy and the reaction measured at different intervals from 24 hr to 28 days. At various time intervals, a biopsy specimen was taken from the reaction site. In TT and BT cases, the erythema was maximum at 48 hr; while the induration was maximum at 21 days. The sequence of the histological changes was built up on the observations made from different cases at varying intervals. The quantum of cellular exudate was high in TT and BT cases as compared to BL and LL cases. The cellular distribution showed loose scattering of cells in the LL and BL types and attempts to form tight clusters in the TT and BT cases. Neutrophils were predominant during the first 48 hr, particularly in the LL, BL, and BT types. By 72 hr the cells were mainly lymphocytic. A tendency for the lymphocytes to cluster around nerve twigs was seen in the TT and BT cases. In the early reaction the quantum of exudate correlated both with erythema and induration; while in the late reaction, it correlated with induration only. The intensity of the early lepromin reaction was more in BT than in TT leprosy, while the induration in the late reaction was more in TT than in BT types. The significance of these findings is discussed.