Current knowledge on cellular interactions in the WG-granuloma

Wegener's granulomatosis (WG) usually starts as granulomatous disease of the respiratory tract (so-called localized WG) before it converts to systemic disease (generalized WG) with the emergence of proteinase 3-specific antineutrophil cytoplasmic autoantibodies (PR3-ANCA) and PR3-ANCA associated autoimmune vasculitis. So far, it remains unresolved how tolerance to "Wegener's autoantigen" PR3 is broken and the immune response to PR3 sustained. Further, the relationship between granulomatous lesions and systemic vasculitis is poorly understood. None of the ANCA-animal-models has reproduced granulomata typical of WG so far. A number of endogenous and exogenous factors (HLA-DPB1*0401 / PTPN22*620W, respiratory epithelial barrier dysfunction? S. aureus, cPR3?) could favour initial formation of granulomata in the respiratory tract and break of tolerance. PR3 induces dendritic cell maturation via the protease activated receptor (PAR)-2 and evokes a strong Th1-type T-cell response in WG. Clusters of PR3⁺ cells (neutrophils /monoctyes) surrounded by antigen-presenting cells, Th1-type CD4⁺CD28^- effector memory T-cells, maturing B- and plasmacells are found in WG-granulomata of the upper respiratory tract. Thus, WG-granulomata might provide the necessary "proinflammatory environment" for the break of tolerance and display features of lymphoid-like tissue neoformation, in which autoimmunity to PR3 could be sustained. Subsequent PR3-ANCA associated systemic vasculitis gives rise to new inflammatory lesions in many other organs, thereby promoting a self-perpetuating pathology characterized by inflammation and autoimmunity to PR3.