An emerging role of neutrophils and NETosis in chronic inflammation and fibrosis in systemic lupus erythematosus (SLE) and ANCA-associated vasculitides (AAV): Implications for the pathogenesis and treatment.

Neutrophils derive from hematopoietic stem cells (HSCs) with systemic inflammation driving their activation and differentiation to myeloid progenitors to ensure enhanced myelopoiesis. Epigenetic reprograming and re-education of these HSCs produces neutrophils primed towards elimination of pathogens and increased inflammatory response. Neutrophils -an important component of acute inflammation- are not present in chronic inflammatory tissues leading to the false assumption that they may not be as important for the latter. Activated neutrophils may release Neutrophil Extracellular Traps (NETs) during a distinct form of cell death, named NETosis; NETs are rich in bioactive molecules that promote thrombosis (including atherothrombosis), inflammation and fibrosis. Thus, although neutrophils may not be present in chronic inflammatory lesions, their remnants may amplify the inflammatory response beyond their short life-span in the tissues. Herein, we review current evidence supporting a role of neutrophils and NETosis in tissue injury and dysfunction in systemic autoimmunity using as disease paradigms Systemic Lupus Erythematosus (SLE) and the ANCA-associated vasculitides (AAV). We also discuss the mechanisms involved and their potential as targets for novel therapy and drug repositioning.