C3a modulates IL-1β secretion in human monocytes by regulating ATP efflux and subsequent NLRP3 inflammasome activation

Abstract

Key Points• C3aR activation increases ATP efflux, NLRP3 inflammasome activation, and IL-1b secretion in human monocytes.• C3aR-activated monocytes drive Th17 responses in vitro and likely in vivo.Interleukin-1b (IL-1b) is a proinflammatory cytokine and a therapeutic target in several chronic autoimmune states. Monocytes and macrophages are the major sources of IL-1b. IL1b production by these cells requires Toll-like receptor (TLR) and adenosine triphosphate (ATP)-mediated P2X purinoceptor 7 (P2X7) signals, which together activate the inflammasome. However, how TLR signals and ATP availability are regulated during monocyte activation is unclear and the involvement of another danger signal system has been proposed. Here, we demonstrate that both lipopolysaccharide (LPS) and the anaphylatoxin C3a are needed for IL-1b production in human macrophages and dendritic cells, while in monocytes, C3a enhanced the secretion of LPS-induced IL-1b. C3a and LPS-stimulated monocytes increased T helper 17 (Th17) cell induction in vitro, and human rejecting, but not nonrejecting, kidney transplant biopsies were characterized by local generation of C3a and monocyte and Th17 cell infiltration. Mechanistically, C3a drives IL-1b production in monocytes by controlling the release of intracellular ATP into the extracellular space via regulation of as-yet unidentified ATPreleasing channels in an extracellular signal-regulated kinase 1/2-dependent fashion. These data define a novel function for complement in inflammasome activation in monocytes and suggest that C3aR-mediated signaling is a vital component of the IL1b-Th17 axis. (Blood. 2013;122(20):3473-3481) IntroductionInterleukin-1b (IL-1b) is a key proinflammatory cytokine involved in host responses to pathogens and tissue injury. IL-1b has gathered substantial interest in recent years because several autoimmune disorders respond specifically to IL-1 receptor blockade using either soluble IL-1 receptor antagonists or blocking monoclonal antibodies (mAbs).1 In addition to inducing neutrophil activation and histamine release by mast cells and maintaining epithelial cell integrity, 2 IL-1b also plays a central role in modulating adaptive effector T-cell responses by preferentially inducing T helper 1 (Th1) and Th17 differentiation.3 In humans, CD4 1 T cells require IL-1b and IL-6 to differentiate into Th17 cells, 4 which contribute to the pathophysiology of inflammatory and autoimmune diseases 5 as well as ischemia reperfusion injury (IRI) and transplant rejection. Monocytes, macrophages, and dendritic cells (DCs) are major IL-1b sources and release this cytokine in response to stimuli such as pathogen-associated or danger-associated molecular patterns (PAMPs or DAMPs) mediated by signaling via several Toll-like receptor (TLR) pathways. 7 Although consensus exists that IL-1b generation requires processing of the 31 K D inactive pro-IL-1b to the 17 K D active form by caspase-1 activation via an inflammasome complex (eg, NLRP3), 8,9 signals leading to NLRP3 and caspase-1 activation are...

Is the Complement Activation Product C3a a Proinflammatory Molecule? Re-evaluating the Evidence and the Myth

“…This view is supported by evidence that C3ar1 2/2 animals have modest pathology reductions in chronic disease models, such as rheumatoid arthritis (40). In contrast to the effects of C3a on purified monocytes (39), in vitro investigations into the effects of C3a on LPSinduced cytokine release by PBMCs demonstrate differences in action depending on the phenotype of the cell. C3a augmented the proinflammatory cytokine production of adherent cells but suppressed that of nonadherent cells (35,36,41).…”

“…C3a also can induce signaling in human monocytes and monocyte-derived macrophages; however, this interaction, with TLR-4 costimulation, induces the production of proinflammatory mediators, such as IL-1b, TNF-a, IL-6, and PGE 2 (35)(36)(37)(38)(39). This suggests that, in the chronic phase of inflammation, where monocyte/macrophage responses become more predominant over neutrophils, C3a may indeed act as a classical proinflammatory mediator.…”

Inflammasomes and its importance in viral infections

“…Destruction of the actin cytoskeleton has also been observed in pyroptotic cells, but the mechanism and importance of this event remain unclear [18,112,113]. Furthermore, during pyroptosis, DNA fragmentation and nuclear condensation occur [13,18,114]. Pyroptosis can efficiently remove infected cells and further stimulates the activation of the immune system via the release of pathogens from the dying cells.…”

Molecular Regulation of Cell Fate in Cerebral Ischemia: Role of the Inflammasome and Connected Pathways

“…The complement subunit C3a has also been demonstrated to regulate NLRP3-mediated IL-1β release in human monocytes by binding to C3a-receptor and via ATP efflux. 53 Moreover, C5a and TNF (tumor necrosis factor) were shown to act as potent primers for cholesterol crystal-induced IL-1β release. Thus, cholesterol crystals use the complement system to induce cytokines and activate the inflammasome.…”