Dermal ultrastructure in leprosy.

We studied the ultrastructure of the dermal inflammatory response in 18 patients with leprosy. Biopsy specimens from 14 lepromatous patients, including four with Lucio's phenomenon and four with erythema nodosum leprosum, were compared with biopsy specimens from one borderline lepromatous and three borderline tuberculoid patients. In all, the dermal infiltrate consisted of macrophages, lymphocytes, and mast cells. This infiltrate was predominantly perivascular, and chronic reactive changes were found in the small dermal vessels. The macrophages contained phagocytized organisms within membrane-bound vacuoles and a wide variety of lysosomal residual dense bodies. Intraendothelial organisms were occasionally seen, especially in biopsy specimens from the patients with Lucio's phenomenon. The greatest number of mast cells were also seen in the infiltrate in those cases. The frequent close association of macrophages with lymphocytes and mast cells suggests an interrelationship between these cells that appears typical of the host response to leprosy.