Ultrastructure of the dermal microvasculature in leprosy.

Infection with M. leprae may lead to the presence of the organism within the dermal vascular endothelium, a phenomenon most pronounced in lepromatous leprosy. In order to study the ultrastructural features of the dermal microvasculature in leprosy, biopsies from 18 patients with lepromatous (14), borderline lepromatous (1) and borderline tuberculoid (3) leprosy were examined. Four patients with Lucio's phenomenon and four with erythema nodosum leprosum were included. The ultrastructural changes in the dermal microvasculature included endothelial swelling and hypertrophy, increased endothelial and pericytic cytoplasmic processes, and pronounced basal lamina reduplication. Occasional large, pale, endothelial cells with widely dispersed organelles were encountered. Phagocytized, membrane-bound intraendothelial organisms were found, similar in appearance to those within dermal macrophages. The predominantly perivascular dermal inflammatory infiltrate consisted of lymphocytes, macrophages and mast cells. The observed ultrastructural changes in the dermal microvasculature are similar to those previously described in the endoneurial vessels. While reflecting nonspecific responses of the dermal microvasculature in chronic inflammation, the findings support a possible role of the small dermal vessels in the chronic nature of the host's response to infection with M. leprae.