Human Eosinophils Recognize Endogenous Danger Signal Crystalline Uric Acid and Produce Proinflammatory Cytokines Mediated by Autocrine ATP

Abstract

Eosinophils are multifunctional leukocytes involved in various inflammatory processes, as well as tissue remodeling and immunoregulation. During inflammation and infection, injured cells and damaged tissues release uric acid and monosodium urate (MSU) crystals as important endogenous danger signals. Uric acid is also implicated in the immunogenic effects of an authentic Th2 adjuvant, aluminum hydroxide. Eosinophils often localize at sites of Th2-type chronic inflammation; therefore, we hypothesized that eosinophils may react to endogenous danger signals. We found that human eosinophils migrate toward soluble uric acid and MSU crystals in a gradient-dependent manner. Eosinophils incubated with MSU crystals, but not those incubated with uric acid solution, produced elevated levels of IL-6 and IL-8/CXCL8. Other cytokines and chemokines, including IL-1β, IL-10, IL-17, IFN-γ, CCL2, CCL3, CCL4, TNF-α, G-CSF, GM-CSF, fibroblast growth factor, vascular endothelial growth factor, and TGF-β, were also produced by eosinophils incubated with MSU crystals. Eosinophils exposed to MSU crystals rapidly (i.e., within 1 min of exposure) released ATP into the extracellular milieu. Importantly, this autocrine ATP was necessary for eosinophils to produce cytokines in response to MSU crystals, and P2 nucleotide receptors, in particular P2Y2, are likely involved in this positive feedback loop. Finally, at higher concentrations, MSU crystals promoted P2R-dependent release of a granule protein (eosinophil-derived neurotoxin) and cell death. Thus, human eosinophils may respond to particulate damage-associated endogenous danger signals. These responses by eosinophils to tissue damage may explain the self-perpetuating nature of chronic inflammation in certain human diseases, such as asthma.

Activation of human fibroblast-like synoviocytes by uric acid crystals in rheumatoid arthritis

“…31 Some studies have demonstrated that uric acid crystals can induce human eosinophils and neutrophils to produce the neutrophil chemokine CXCL8. 32,33 To examine whether uric acid crystals also modulate the expression of chemokines in FLS, we found that monosodium urate crystals were able to significantly increase the release of the chemokine CXCL8 from both control FLS and RA-FLS (P,0.05). Combined treatment of monosodium urate crystals with TNF-a or IL-1b resulted in the synergistic production of CXCL8 from control FLS (Figures 3 and 4).…”

Interleukin-17 cytokine signalling in patients with asthma

“…Until recently, there was no functional evaluation of this potentially important finding. However, there is now a study from KOBYASHI et al [47] suggesting that isolated human blood eosinophils harvested from healthy volunteers can release IL-17A protein, albeit in response to crystals of monosodium, a stimulus of unclear relevance for human asthma.…”

Purinergic signaling in inflammatory cells: P2 receptor expression, functional effects, and modulation of inflammatory responses

“…These effects occur through Ca 2+ mobilization [19,194,195]. ATP can either interact directly with P2X ion channels or indirectly activate [196] IL-6 and IL-8 [197] by P2Y 2 receptor stimulation, while P2X1, P2X7, and P2Y 6 receptors might also be implicated in the release of IL-8 [196]. The P2Y 2 receptor subtype expressed on eosinophils is also suggested to be implicated in eosinophil chemotaxis [141,193].…”

“…Also endothelial P2Y 2 receptors can affect eosinophil migration by regulating the expression of endothelial VCAM-1 which mediates migration and adhesion of eosinophils via the α4β1 integrin [193]. Monosodium urate (MSU) crystals induce the release of autocrine ATP from eosinophils which provides a pivotal positive feedback signal via P2 receptors on eosinophils [197]. DAMP damage-associated molecular patterns, PAMP pathogen-associated molecular patterns, VCAM-1 vascular cell adhesion molecule 1.…”

“…The same researchers translated their findings into an in vivo model showing A3 and P2Y2 receptors to control the recruitment of neutrophils to the lung in a mouse model of sepsis [35,56]. The involvement [10,19,191,192] Chemotaxis P2Y 2 [141,193] Release of chemokines and cytokines P2Y 2 , P2X1, P2X7, and P2Y 6 [196,197] Ambiguous data reporting the ATP to be a long-range chemoattractant without phagocytic activity [115] vs. ATP as an autocrine/paracrine signal limited to influence chemotaxis but accompanied with phagocytosis by locally inducing lamellipodial membrane extensions [117,118] of the neutrophilic P2Y 2 receptor in neutrophil migration was corroborated by several other research papers by the group of Sévigny who described that P2Y 2 receptor activation on neutrophils is required for IL-8 (released from monocytes/macrophages and/or epithelial cells at sites of inflammation) to induce most efficient neutrophil chemotaxis [57], and that P2Y 2 receptors on neutrophils are implicated in the potentiation of IL-8 production by human neutrophils themselves, a mechanism under tight control by the ectonucleotidase "Ecto-nucleoside triphosphate diphosphohydrolase 1" (E-NTPDase1 or CD39) expressed on the surface of neutrophils [58]. E-NTPDase1 also regulates the migration speed of neutrophils but not their ability to detect the orientation of the gradient field generated by fMLP that induces an autocrine ATP release via stimulation of the formyl peptide receptor [59].…”