Anti-proteinase 3 antibodies (Anti-PR3)

The test is used to diagnose Wegener's granulomatosis. Proteinase 3 is a small protein localized in neutrophils, monocytes and cytoplasm of endothelial cells. It is one of the major antigens of antibodies to the cytoplasm of neutrophils. Detection of antibodies to proteinase 3 is a highly specific laboratory test in the diagnosis of granulomatosis with polyangiitis (formerly called Wegener's granulomatosis), a severe disease manifested by a triad with granulomatous involvement of the nasopharynx, respiratory tract, lungs, and kidneys. This disease is often accompanied by polyneuritis. High titers of antibodies to proteinase 3 are found in 90-95% of patients with a detailed picture of active granulomatous process. Localized forms of Wegener's granulomatosis affecting the upper respiratory tract are less often accompanied by autoantibodies (50-60%). Rarely, antibodies to proteinase 3 may be found in other ANCA-associated vasculitis which are microscopic polyangiitis, Churg-Strauss syndrome, and polyarteritis nodosa.

The content of antineutrophil antibodies in Wegener's granulomatosis is clinically significant and correlates with disease activity. High titer serves as a basis for pathogenetic immunosuppressive therapy. To increase the sensitivity of serologic examination of patients with systemic vasculitis, current international recommendations require the simultaneous use of immunofluorescence test for detection of antibodies to neutrophil cytoplasm, as well as detection of antibodies to the main antigens which are proteinase 3 and antibodies to myeloperoxidase.