[Vasculitis--aspect of cellular and molecular pathogenesis]

Vasculitis, inflammation of the vessel wall, can be observed in acute and chronic inflammatory processes, in vascular rejection of allogeneic transplants and can be encountered as primary vasculitis of arterial, arteriolar, capillary and venular vessels. Although the numerous forms of vasculitis and their associations with different diseases result in a multitude of etiologic and pathogenetic factors there are pathogenetic factors common to several vasculitides. These include innate immunity factors, transcription factors such as NFkB, endothelial cytoprotective agents such as NO and anti-neutrophilic cytoplasmic auto-antibodies (ANCA). ANCA may be directed against several antigens, in the majority of cases against proteinase 3 and myeloperoxidase. The complex of proteinase 3 and ANCA leads to an increased expression of CD18, CD14 and an elevated synthesis of cytokines and chemokines such as interleukin 1, interleukin 8 in monocytes. In granulocytes generation of reactive oxygen species is found in addition. In both cells apoptosis finally occurs. ANCA may also bind to a surface glycoprotein (gp130) expressed on glomerular and peritubular endothelia in the kidney. Thus the activation of granulocytes, monocytes and endothelial cells by ANCA may be a critical step in the initiation phases of vasculitis. NO is cytoprotective for endothelial cells in small concentrations. Our group has shown in detailed studies that inhibition of endothelial NO synthase is detrimental and enhancement of activity of endothelial NO synthase is beneficial for allogeneic solid organ transplants. The transcription factor complex NFkB is a key regulatory transcription factor for the expression of genes and proteins associated with acute inflammatory processes and endothelialitis. Inhibition of NFkB activity by a decoy-oligonucleotide prevented activation of endothelial calls in reperfusion injury and vascular rejection. The complement system probably plays an essential role in the initiation and propagation phases of vasculitis. Specifically the pneumococcal C-polysaccharide-reactive protein (CRP), synthesized after trauma and infection, can potently activate the complement cascade which leads to an activation of endothelial cells with increased expression of adhesion molecules. The 4 shortly described pathogenetic mechanisms of vasculitis seem to be important and common factors for the generation and maintenance of vascular inflammation; nevertheless these factors are only part of the spectrum of different humoral and cellular responses in vasculitis. The described experimental investigations on endothelial damage and endothelialitis may lead to new therapeutic strategies in vasculitis.