Mast cells in leprosy and leprosy reaction

Mast cells can be visualized in routine, acid-fast-staining, paraffin tissue section as metachromatic staining cells, and can be activated to release inflammatory mediators which play a role in the cell-mediated immune response.

Skin biopsy tissues were taken from the most active skin lesion of each leprosy patient at the time of diagnosis (nonreactional group) and at the time of reaction (reactional group) during the years 1994-1997 in the leprosy clinic at the Department of Dermatology, Faculty of Medicine, Siriraj Hospital, Mahidol University, Thailand. Mast cells were identified by metachromatic staining (purple) in Fite's stain sections and reported as the average number of cells per high power field in three compartments: at the center and periphery of the granuloma and in the interstitium. The data were analyzed in three groups: nonreactional group, type I, and type II leprosy reactions. The mast cell count of each group and each compartment of the section, expressed as the mean +/- standard error, was compared.

A total of 95 persons were included in the study, but 108 tissue sections were obtained due to nine cases having more than one section. Of these patients, 63 cases (66.32%) had no reaction, 19 cases (20%) had type I reaction, and 13 cases had type II reaction. There was no difference in age and sex among these groups. The mast cell count in the interstitium was higher than that within the granuloma, both at the center and at the periphery, in every type, and the count in this area reduced significantly in leprosy reactions, both type I and type II, compared with the nonreactional group.

The change in the average mast cell number in nonreactional leprosy and leprosy reactions may indicate the important role of mast cells in dynamic changes in the cell-mediated immune response in leprosy and leprosy reactions.