Neutrophil Extracellular Traps Activate Proinflammatory Functions of Human Neutrophils

Abstract

Neutrophil extracellular traps (NETs) consist of decondensed nuclear chromatin that is associated with proteins and are released by neutrophils during an inflammatory response. Released NETs are able to capture pathogens, prevent their dissemination and potentially kill them via antimicrobial peptides and proteins that are associated with the decondensed chromatin. In addition to their antimicrobial functions, NETs have also been shown to exert immunomodulatory effects by activation and differentiation of macrophages, dendritic cells and T cells. However, the effect of NETs on neutrophil functions is poorly understood. Here we report the first comprehensive study regarding the effects of NETs on human primary neutrophils in vitro. NETs were isolated from cultures of PMA-exposed neutrophils. Exposure of neutrophils to isolated NETs resulted in the activation of several neutrophil functions in a concentration-dependent manner. NETs induced exocytosis of granules, the production of reactive oxygen species (ROS) by the NADPH oxidase NOX2, NOX2-dependent NET formation, increased the phagocytosis and killing of microbial pathogens. Furthermore, NETs induced the secretion of the proinflammatory chemokine IL-8 and the B-cell-activating cytokine BAFF. We could show that the NET-induced activation of neutrophils occurs by pathways that involve the phosphorylation of Akt, ERK1/2 and p38. Taken together our results provide further insights into the proinflammatory role of NETs by activating neutrophil effector function and further supports the view that NETs can amplify inflammatory events. On the one hand the amplified functions enhance the antimicrobial defense. On the other hand, NET-amplified neutrophil functions can be involved in the pathophysiology of NET-associated diseases. In addition, NETs can connect the innate and adaptive immune system by inducing the secretion of the B-cell-activating cytokine BAFF.

Neutrophil Extracellular Traps, Angiogenesis and Cancer

“…However, there is some evidence that neutrophils and NETs also exert reparative effects in the context of tumor inflammation [ 198 , 213 ]. Moreover, recent studies indicate that different components of NETs can propagate [ 245 , 246 ] or modulate inflammation [ 247 ]. Such dichotomy in the outcome of neutrophil activity is fascinating and intriguing [ 282 ].…”

“…Increasing evidence demonstrates that NETs can promote inflammation by inducing proinflammatory cytokines from different immune cells [ 245 , 246 ]. In particular, histones, the major citrullinated proteins in NETs, activate the transcription of IL-1β in mononuclear cells by binding and activating TLR4.…”

“…Moreover, NET DNA synergizes with citrullinated histones to induce IL-1β by promoting intracellular TLR4 translocation to endosomes [ 245 ]. In addition, NETs isolated from activated human neutrophils resulted in the activation of several cellular functions [ 246 ]. In particular, NETs induced the secretion of CXCL8/IL-8, but not of TNF-α, by human neutrophils.…”

Alpha-1-antitrypsin binds to the glucocorticoid receptor with biological significance in macrophages

“…But could AAT have effects in other cell types that are beneficial in the context of TB? One possibility is that AAT antagonizes the damaging effects of neutrophils in the later stages of TB (Lowe et al, 2012) by: (i) sequestering IL-8 (Bergin et al, 2010), inhibiting neutrophil chemotaxis (McCarthy et al, 2016), and, as we have shown, inhibiting IL-8 production via binding to GR and (ii) inhibiting formation of neutrophil extracellular traps (NETs) -which are elastase-and IL-8induced extruded DNA decorated with citrullinated histones, elastase, and other proteinsmeant to capture extracellular bacteria but may also contribute to tissue injury (de Melo et al, 2018;Dömer et al, 2021;Frenzel et al, 2012;Wartha et al, 2007). AAT has also been shown to cause decreased shedding of macrophage mannose receptors (MMR), increasing their cell surface expression and reducing soluble MMR, effects which may contribute to the antiinflammatory effects of AAT (Embgenbroich et al, 2021;Serban et al, 2017).…”

Crosstalk between B cells and neutrophils in rheumatoid arthritis

“…ICs are powerful stimuli of NET release (e.g., [ 22 , 67 , 68 ). In addition, NETs stimulate neutrophils to produce further NETs and to secrete IL‐8 and BAFF [ 69] , promoting the vicious circle between B cells and neutrophils (Figure 1 ).…”