Free subepidermal grenz zone (band of Unna) in lepromatous leprosy. Histological and ultrastructural findings.

Although the grenz zone is indeed free of typical leprosy cells with giant lysosomes, it is not free from leprosy bacilli--these are found in slightly infested macrophages and fibroblasts. For that reason, it would be much clearer if we simply called this region the subepidermal grenz zone of lepromatous leprosy. The subepidermal grenz zone is not pathognomonic of leprosy since grenz zones can be found in other diseases as well. Whereas the grenz zone is typical in lepromatous leprosy, it is not necessarily characteristic of the borderline or the tuberculoid form of the disease. The light and electron microscopical structure of the grenz zone shows that the formation of the subepidermal grenz zone cannot be explained by any particular pathogenetic principle on which therapy can be based.