Neutrophil extracellular traps exacerbate Th1‐mediated autoimmune responses in rheumatoid arthritis by promoting DC maturation

Abstract

Aberrant formation of neutrophil extracellular traps (NETs) is a key feature in rheumatoid arthritis (RA) and plays a pivotal role in disease pathogenesis. However, the mechanism through which NETs shape the autoimmune response in RA remains elusive. In this study, we demonstrate that inhibition of peptidylarginine deiminases (PADs) activity in collagen-induced arthritis (CIA) mouse model significantly reduces NET formation, attenuates clinical disease activity and prevents joint destruction. Importantly, PAD4 blocking markedly reduces the frequency of collagen-specific IFN-γ producing T helper 1 (Th1) cells in the draining lymph nodes (dLNs) of immunized mice. Exposure of dendritic cells (DCs) to CIA-derived NETs induces DC maturation characterized by significant upregulation of costimulatory molecules, as well as elevated secretion of IL-6. Moreover, CIA-NET-treated DCs promote the induction of antigen-specific Th1 cells in vitro. Finally, NETs from rheumatoid arthritis (RA) patients showed an increased potential to induce the maturation of DCs from healthy individuals, corroborating the findings obtained in CIA mouse model. Collectively, our findings delineate an important role of NETs in the induction and expansion of Th1 pathogenic cells in CIA through maturation of DCs and reveal a novel role of NETs in shaping the RA-autoimmune response that could be exploited therapeutically.

Antibody Responses to Citrullinated and Noncitrullinated Antigens in the Sputum of Subjects With Rheumatoid Arthritis and Subjects at Risk for Development of Rheumatoid Arthritis

“…In this study, we cannot determine whether immunogenic proteins on NETs triggered local autoantibody generation or if local autoantibodies triggered increased NETs. However, findings from several recent studies support the hypothesis that NETs could trigger ACPA, including that NETs can themselves trigger immune responses associated with autoimmunity(39), that NETs in lupus patients can alter the structure and function of proteins including apolipoproteins(40), and that the uptake of NET proteins by antigen presenting cells is associated with systemic ACPA(8). …”

Protein arginine deiminase 4 inhibition is sufficient for the amelioration of collagen-induced arthritis

“…This suggests that PAD4 activity does not regulate autoantibody production to collagen epitopes directly. Indeed, a recent paper [53] reproduces the efficacy of Clamidine in CIA and demonstrates elegantly that it is associated with marked decreases in the numbers of neutrophils undergoing NETosis (assessed robustly by quantification of co-stained images). Importantly, mice treated with GSK199 did not show reduced reactivity to citrullinated peptides specifically, but demonstrated reduced reactivity to a subset of both citrullinated and native peptides, as we observed with pan-PAD inhibition.…”

“…In concert with the growing literature in this field, these potential mechanisms are varied, but may include the regulation of complement protein activation and/or deposition in the joint (described herein), T helper cell activity [60], dendritic cell maturation [53] or other proinflammatory pathways known to participate in this disease process [62]. However, GSK199 treatment does not appear to reduce total citrulline levels or anti-mouse CII autoantibody titres.…”

Mechanisms and disease relevance of neutrophil extracellular trap formation

“…[43][44][45][46][47] In contrast, PMA-driven NET formation may not require PAD4, 48 and PAD4 inhibition does not affect the formation of NETs in response to cholesterol crystals. 49 Similarly, while PAD4 inhibition alleviates symptoms in mice with collageninduced arthritis, 43,50 preventing NET formation with PAD4 inhibitors has not been effective in the K/BxN autoantibody-mediated arthritis mouse model. 51 Data obtained with Cl-amidine, or its derivatives, should be viewed with caution because these inhibitors are not specific for PAD4, but rather target all PAD isotypes.…”