Monocyte‐derived neutrophil chemotactic factor/interleukin‐8 is a potential mediator of crystal‐induced inflammation

Abstract

The physical interaction of particulates with resident mononuclear phagocytes is a consistent feature in certain forms of crystal-induced inflammation. In this study, we observed that monosodium urate crystals stimulated the rapid release of neutrophil chemotactic activity from monocytes, and that this activity steadily increased over 24 hours. Because the release of monocytederived neutrophil chemotactic activity was markedly diminished by pretreatment of the monocytes with cycloheximide, and was completely removed from conditioned media by adsorption to heparin-agarose, we addressed the possibility that monocyte-derived neutrophi1 chemotactic factor/interleukin-8 (IL-8), a heparinbinding neutrophil-activating polypeptide, might modulate these activities. Urate crystal-induced IL-8 secretion from monocytes was verified by radioimmuno- assay. In addition, an IL-%specific antibody markedly inhibited the neutrophil-activating capacity of the conditioned media from monocytes activated by urate crystals, as well as by inflammatory silica crystals. Last, IL-8 was significantly increased in gouty synovial fluids (range 3.0-16.8 ng/ml, mean 8.4 ng/ml, n = 6) relative to osteoarthritic synovial fluids (range 1.1-1.7 nglml, mean 1.5 ng/ml, n = 6) (P = 0.006). We conclude that microcrystal-induced secretion of IL-8 by mononuclear phagocytes may mediate a number of forms of crystalinduced inflammation.

Innate immunity conferred by toll-like receptors 2 and 4 and myeloid differentiation factor 88 expression is pivotal to monosodium urate monohydrate crystal-induced inflammation

“…All chemical reagents were obtained from Sigma-Aldrich (St. Louis, MO), unless indicated otherwise. Triclinic MSU crystals were prepared under pyrogen-free conditions, using uric acid pretreated for 2 hours at 200°C prior to crystallization (10). The crystals were suspended at 25 mg/ml in sterile, endotoxin-free phosphate buffered saline (PBS), and verified to be free of detectable lipopolysaccharide contamination (Ͻ0.025 endotoxin units/ml) by the Limulus amebocyte cell lysate assay (BioWhittaker, Walkersville, MD).…”

“…Subcutaneous pouches were generated by the injection of sterile, filtered air to create an accessible space that developed a synovium-like membrane within 7 days, as previously described (10). Briefly, anesthetized 10-12-week-old WT, TLR-2 Ϫ/Ϫ , TLR-4 Ϫ/Ϫ , and MyD88 Ϫ/Ϫ mice were injected with 5 ml of sterile air into the subcutaneous tissue of the back, followed by a second injection of 3 ml of sterile air into the pouch 3 days later.…”

“…Neutrophil chemotactic CXCR2-binding chemokines, including keratinocyte-derived cytokine (KC)/growth-related oncogene ␣ (GRO␣)/CXCL1 and IL-8/CXCL4 (10), appear to be absolutely essential for the neutrophil-dependent inflammation triggered by the MSU crystals, as demonstrated previously in CXCR2 Ϫ/Ϫ mice (11). Release of the neutrophilexpressed calgranulin heterodimer S100A8/A9, one of the most abundant protein constituents of the neutrophil cytoplasm (12), appears to substantially amplify neutrophil recruitment in gouty inflammation (13).…”

Crystal‐induced neutrophil activation. II. evidence for the activation of a phosphatidylcholine‐specific phospholipase D

“…The interaction between inflammatory crystals and neutrophils is accompanied by a variety of cellular and biochemical changes, including release of lysosomal enzymes, production of superoxide anions and of 5-lipoxygenase products (e.g., leukotriene B4), and synthesis of a phospholipase A, activating-protein and of cytokines such as interleukin-1 and interleukin-6 (7-15). Recently, microcrystals have also been shown to stimulate the synthesis of interleukin-8 (16) and tumor necrosis factor a (17) in monocytes. Rapid increases in levels of cytosolic free calcium after exposure of neutrophils to microcrystals have also been described ( I 1 , 18,19).…”

Safe disposal of inflammatory monosodium urate monohydrate crystals by differentiated macrophages

“…A beneficial role of monocyte/macrophages, however, is difficult to reconcile with the fact that monocytes, when challenged with urate crystals, secrete tumor necrosis factor ␣ (TNF␣) (6,7), interleukin 1␤ (IL-1␤) (8), , and IL-8 (10). This in turn activates expression of endothelial cell adhesion molecules (Eselectin, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1), which leads to secondary neutrophil recruitment to sites of crystal deposition (11)(12)(13).…”