Ultrastructural study across the leprosy spectrum.

We have carried out a systematic ultrastructural study of the bacilli, the cell-mediated response in the host, and the dermal microvasculature in lepromatous (LL), borderline lepromatous (BL), and borderline tuberculoid (BT) types of active leprosy (eight cases). In the types of least resistance (LL and BL), macrophages with large cytoplasmic processes were observed; in addition, numerous peripheral vacuoles were found in BL. Mast cells were abundant and vascular alterations constant. BT macrophages showed more regular outlines and multivacuolated cytoplasms with plentiful rough endoplasmic reticulum. Giant cells were scarce. Bacilli, both isolated and in globi, were contained within the vacuoles and appeared constantly in macrophages and endothelial and Schwann cells in LL and BL. Conversely, in BT they were found singly, infrequently in the endothelial cells, and not at all in Schwann cells. Forms in the process of destruction or degradation were more common than intact forms, in which the symmetric outline of the membrane could be seen clearly.