Association of alkaline phosphatase with an autoantigen recognised by circulating anti-neutrophil antibodies in systemic vasculitis.

A solid phase radioimmunoassay has been developed to detect circulating autoantibodies to neutrophil cytoplasmic antigens in systemic vasculitis. After fractionation of these antigens by size, with gel filtration high performance liquid chromatography, sera from patients with clinically different forms of systemic vasculitis, Wegener's granulomatosis (WG) and microscopic polyarteritis (MP), showed contrasting specificities of binding. WG sera bound to 100, 6.2, and 1.8 kD components, whereas MP sera bound only to the 100 kD component, allowing immunological distinction between the syndromes. The 100 kD component recognised by both WG and MP sera also showed alkaline phosphatase activity. Further evidence for this association was obtained by direct binding experiments between systemic vasculitis sera and calf-intestinal or human neutrophil alkaline phosphatase and by the cross-reactivity of W8, a monoclonal antibody raised to a neutrophil cytoplasmic autoantigen, with various preparations of the enzyme.