Cutaneous and systemic vasculitis: cellular players and pathogenetic aspects.

Vascular wall damage, inflammatory cell recruitment and subsequent structural remodelling define a vasculitic process. Histopathological classification of vasculitis is based on the caliber of the vessel involved and on the prevalent type of inflammatory cells (neutrophils in acute forms, lymphocytic for chronic, histiocytic for granulomatous). A large amount of information is emerging from the literature on the complex pathophysiology of the cellular components of vessel wall. For instance, endothelial cells not only have the task to cover the inner surface of the vascular system but they also play an active role in tuning the immunological response in a very sophisticated way. Neutrophils are not only terminally differentiated cells sacrificed for a valuable cause. Cellular types of the perivascular microenvironment play roles one time not expected. The spread of the inflammatory process into the vascular wall is not necessarily inside-out. These and other selected concepts will be discussed in this paper.