Pathogenesis of leukocytoclastic vasculitis.

There is compelling animal and human experimental evidence that leukocytoclastic vasculitis is a hypersensitivity vasculitis, similar in nature to the experimental Arthus reaction. The immune complexes formed in antigen excess circulate until some event occurs that cause deposition in blood vessel walls. Adhesion molecules and cytokines released by endothelial cells and activated neutrophils represent a key factor in this process. The membrane attack complex of complement plays a significant role in altering the endothelial cell membrane integrity. Activated neutrophils release proteolytic enzymes, especially collagenases and elastases, along with free oxygen radicals that damage the vessel walls and the surrounding tissues. It remains uncertain whether antineutrophilic cytoplasmic antibodies, anti-endothelial antibodies and anti-cardiolipin antibodies are epiphenomena or are directly involved in the disease process. Apoptotic cell death mediated by the Fas/Bc12 system is a feature of leucocytoclastic vasculitis. In conclusion, the post-capillary venule is the active orchestrator of neutrophils in leukocytoclastic vasculitis which mediate a complex series of endothelial/leukocyte interactions.