Silicon exposure and vasculitis.

A combination of risk factors are involved in susceptibility to a primary or secondary form of vasculitis. Most forms of vasculitis are probably genetically based but environmentally triggered. This review discusses currently available evidence for a pathophysiologic role of one possible environmental trigger, silica. Since 1960, several patients with pulmonary silicosis have been described that developed pauci-immune necrotizing crescentic glomerulonephritis, i.e., with either completely negative immunofluorescence findings or nonspecific granular IgM or C3 deposits along the capillary wall. Recently it was reported that these patients have antineutrophil cytoplasmic antibodies (ANCAs) that are in most cases directed to myeloperoxidase. Further, patients with pulmonary silicosis may develop microscopic polyangiitis, the syndrome of lung hemorrhage and nephritis, or Wegener's granulomatosis. To further substantiate the relation between silicon exposure and renal failure or vasculitis, several case-control studies have been reported. Exposure to silicon-containing compounds was found to be related to chronic renal failure (odds ratio, 1.7:2.5) or vasculitis (odds ratio, 6.5:14.0). The mechanisms by which silica may induce ANCA-associated glomerulonephritis or vasculitis are not well known. Silicon-containing compounds have a pronounced adjuvant effect on immune responses, and silica particles are potent stimulators of lymphocytes and monocytes or macrophages. Further, silica may induce apoptosis of monocytes or macrophages and possibly neutrophils. In conclusion, at present there is ample evidence that occupational exposure to silicon-containing compounds is related to the development of ANCA-associated glomerulonephritis and vasculitis, and silica is one of the first well-documented environmental triggers in these diseases.