Muramidase (lysozyme) findings in sural and radial nerve biopsies in leprosy patients after varying periods of treatment.

Using the immunoperoxidase staining method, tissue muramidase (lysozyme) activity was studied in 34 nerve biopsies from leprosy patients and compared to findings in the skin. In a majority of lepromatous and borderline-lepromatous leprosy patients, the enzyme was seen to form a saccular pattern within the cells; whereas a granular pattern was found at the tuberculoid end of the leprosy spectrum, as well as during reversal reactions. Indeed, the most intense enzymatic activity was found in four patients with reversal reactions. Compared to the skin, muramidase activity was found to be more intense and persisted longer in the nerves. Successful antileprosy treatment reduced the enzymatic activity in both the nerves and the skin, but more so in the skin. Schwann cells and axons did not show muramidase activity, indicating that the muramidase-positive cells are not of neuronal origin. Our results suggest that a high percentage of mononuclear cells infiltrating the peripheral nerves in leprosy are derived from blood monocytes. The function of tissue muramidase in leprosy is not yet clear. Its peculiar intracellular distribution pattern in the different forms of leprosy, however, warrants further study to elucidate its role in the pathogenesis of the disease.