Neutrophil activation and B-cell stimulation in the pathogenesis of Felty's syndrome

Felty's syndrome (FS) is a severe arthritic disorder that features chronic neutrophil activation and progresses to neutropenia and susceptibility to unabated infections. The life-threatening manifestations of FS have focused the attention of clinical experimenters who have made persistent efforts to find new and effective therapies. This review highlights important milestones in the research on FS and draws attention to recent studies on the antigen specificity of antibodies present in patients' sera. Recent data have indicated that immunoglobulins G (IgGs) in patients with FS bind selectively and specifically to deiminated histones and neutrophil extracellular chromatin traps (NETs). Deimination is the conversion of certain arginine residues in proteins to citrullines by the enzyme peptidylarginine deiminase 4. Earlier observations had indicated that IgGs in FS patients avidly bind to citrullinated peptides. These observations suggest that NETosis, the type of cell death that is defined by the release of NETs, provides autoantigens that stimulate B cell responses in this patient group. This insight parallels recent observations in other autoimmune conditions and lends support to the paradigm that NETosis plays a leading role in the pathogenesis of antiself immune responses.