Proteinase 3, protease-activated receptor-2 and interleukin-32: linking innate and autoimmunity in Wegener's granulomatosis

Proteinase 3 (PR3) is a multifunctional neutrophil-derived serine protease influencing cell cycle, differentiation, and cell death. This molecule is the main target antigen of autoantibodies in Wegener's granulomatosis (WG) known as antineutrophil cytoplasmic antibodies (PR3-ANCA). WG usually starts as granulomatous inflammation of the upper respiratory tract (localized phase) and progress to systemic disease with PR3-ANCA-associated vasculitis (generalized phase). PR3-ANCA is thought to play a critical role in the pathogenesis of vascular damage in WG. In contrast, it is not clear how the granulomatous inflammation, the hallmark of WG, is driven, and what is the relationship between granuloma and autoimmunity. Recent findings provide evidence that PR3 might function as endogenous "danger/alarm" signal that communicates the presence of tissue injury to dendritic cells (DC) via protease-activated receptor-2 (PAR-2), triggers their maturation and instructs DC to induce Th1-type cell responses in WG. Furthermore, PR3 has the capacity to bind and activate IL-32, a recently discovered proinflammatory cytokine that has emerged as an important player in innate and adaptive immune response.Collectively, these results delineate new pathogenic pathways at the molecular level and provide insights into the mechanisms by which PR3 may contribute to the early pathogenesis of WG supporting the pivotal role of the interaction of Wegener's autoantigen with the "gateway" receptor PAR-2 in mediating both innate and adaptive immune response in WG.