Neutrophil extracellular traps mediate transfer of cytoplasmic neutrophil antigens to myeloid dendritic cells toward ANCA induction and associated autoimmunity

Abstract

Antineutrophil cytoplasmic antibodies (ANCAs) target proteins normally retained within neutrophils, indicating that cell death is involved in the autoimmunity process. Still, ANCA pathogenesis remains obscure. ANCAs activate neutrophils inducing their respiratory burst and a peculiar form of cell death, named NETosis, characterized by formation of neutrophil extracellular traps (NETs), decondensed chromatin threads decorated with cytoplasmic proteins endorsed with antimicrobial activity. NETs have been consistently detected in ANCA-associated small-vessel vasculitis, and this association prompted us to test whether the peculiar structure of NET favors neutrophil proteins uploading into myeloid dendritic cells and the induction of ANCAs and associated autoimmunity. Here we show that myeloid DCs uploaded with and activated by NET components induce ANCA and autoimmunity when injected into naive mice. DC uploading and autoimmunity induction are prevented by NET treatment with DNAse, indicating that NET structural integrity is needed to maintain the antigenicity of cytoplasmic proteins. We found NET intermingling with myeloid dendritic cells also positive for neutrophil myeloperoxidase in myeloperoxidase-ANCA-associated microscopic poliangiitis providing a potential correlative picture in human pathology. These data provide the first demonstration that NET structures are highly immunogenic such to trigger adaptive immune response relevant for autoimmunity.

Gender differences in circulating levels of neutrophil extracellular traps in serum of multiple sclerosis patients

“…The activation of DCs by NETs appears to play an important role in the pathogenesis of some autoimmune diseases such as psoriasis (Lande et al, 2007), systemic lupus erythematosus (SLE) (Barrat et al, 2005;Garcia-Romo et al, 2011;Lande et al, 2011;Means et al, 2005) small vessel vasculitis (Sangaletti et al, 2012) and type I diabetes (Diana et al, 2013). NETsactivated pDCs produce large amounts of interferon that can lead to the maturation of myeloid DCs (mDCs) and exert an effect on T cell function.…”

“…In SLE, pathogenic auto-antibodies have been associated with abnormal clearing of NETs and NETosis that results in abnormally high production and/or low degradation of NETs, which then leads to tissue damage and facilitated generation of large quantities of auto-antibodies creating a vicious cycle (Knight and Kaplan, 2012). In small vessel vasculitis, NETs can favor neutropil proteins uploading into mDCs and the induction of anti-neutrophil cytoplasmic antibodies (ANCAs) (Sangaletti et al, 2012). Recently, we demonstrated that NETs are also able to directly prime T cells by reducing their activation threshold, which represents a novel link between innate and adaptive immune responses .…”

“…NETosis, the process of neutrophil cell death that leads to expulsion of NETs, can be triggered by different stimuli including pro-inflammatory cytokines such as IL-8 and TNFα, phorbol 12-myristate 13-acetate (PMA) (Brinkmann et al, 2004;Fuchs et al, 2007), activated platelets (Clark et al, 2007) and endothelial cells (Gupta et al, 2010), and placental microparticles (Gupta et al, 2005). In addition to their bactericidal potential, NETs can also activate plasmacytoid-(pDCs) (GarciaRomo et al, 2011;Lande et al, 2011) and myeloid (mDC) (Sangaletti et al, 2012) dendritic cells and in consequence modulate inflammatory responses. …”

Defective Stromal Remodeling and Neutrophil Extracellular Traps in Lymphoid Tissues Favor the Transition from Autoimmunity to Lymphoma

“…In addition, the functional link between NETosis and CD5 + B-cell proliferation was independent of the Fas or Sparc genotype; neutrophils from wild-type (WT) spleens were able to stimulate CD5 + B-cell proliferation following induction of NETosis with PMA (ref. 29 ; Fig. 4B ).…”

“…29 ). In addition, NETosis requires myeloperoxidase (MPO) expression ( 30 ), which was increased in the spleens of lpr/lpr/ Sparc −/− mice with NET-like extracellular structures ( Fig.…”