Ultrastructural aspects in skin allergic vasculitis

Twelve cases of skin allergic vasculitis were electronmicroscopically studied. The most striking changes were noticed at the level of capillaries, whose wall components were all affected, especially the endothelial cells. These presented at first adaptive changes, with swelling, microvillosities of plasmalemma protruding into the lumen, and many pinocytotic vesicles showing an intensely active transport. Followed different degrees of degenerative changes of cytoplasms and nuclei, the junctional complexes being interrupted, even discontinuous. The pericytes showed similar changes. The basement membrane was thickened, nonhomogeneous, with a spongy aspect, small discontinuities and some electron-dense depots. The endothelial cell damage and the discontinuity of basement membranes, as well as the alteration of pericytes allowed the migration of blood cells into interstitial spaces, followed by leucocytoclasia. As a consequence, in the perivascular tissue a polymorphous cellular infiltrate developed. The mechanisms and significance of these changes are discussed.