Autoantibodies to neutrophil cytoplasmic enzymes in Felty's syndrome.

In this study we determined the occurrence of anti-neutrophil cytoplasmic antibodies (ANCA) and the specificity of these antibodies (Ab) in the serum of patients with Felty's syndrome (FS) and in serum of patients with uncomplicated rheumatoid arthritis (RA). ANCA, detected by indirect immunofluorescence on ethanol-fixed neutrophils, was found in 77% of 30 patients with FS and in 36% of 50 RA patients. Ab against lactoferrin (LF) occurred more frequently in FS patients (50%) than in RA patients (4%), whereas reactivity against the other cytoplasmic antigens tested (proteinase-3, myeloperoxidase and elastase) did not differ significantly between these patient groups. The specific reactivity of FS sera with LF was established by demonstrating that the Ab reactivity resided in IgG, was located in the F(ab')2 fragments and could be inhibited from binding to the ELISA plate-bound LF by purified LF in the fluid phase. These results demonstrate that anti-LF Ab occur in FS and suggest that the detection of anti-LF Ab in patients with FS may be useful in the diagnosis of FS.