Anti-neutrophil cytoplasm antibodies in patients with monoclonal gammopathies

Anti-neutrophil cytoplasm antibodies (ANCA) are specific markers for systemic vasculitis. In view of the autoreactivity to other autoantigens reported in patients with monoclonal immunoglobulins (MIg), the reactivity of 150 sera from 125 patients with MIg was tested for ANCA by radioimmunoassay (RIA) with inhibition stage and indirect immunofluorescence (IIF). Seven were positive for IgG ANCA, all with IgG MIg and 5 were positive for IgM ANCA, 4 with IgM MIg and 1 with IgG MIg. No IgA ANCA were found. The patterns seen on IIF were identical to those seen with sera from patients with systemic vasculitis and were cytoplasmic in 6 and peri-nuclear in 6. The restriction of the ANCA activity to the MIg was studied in six sera by light chain specific RIA, and anion exchange fractionation of the sera. The ANCA activity appeared to be polyclonal in at least three sera and could be found in the monoclonal fraction in only three patients. Associated autoimmune diseases were found in some of these ANCA positive patients including Sjögren's syndrome, MacDuffie hypocomplementemic vasculitis and rheumatoid polyarthritis but the classical vasculitic features normally associated with ANCA were not observed. We conclude that ANCA is a further autoreactivity present in some sera with MIg and discuss the relation between monoclonal gammopathies and autoimmunity.