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Objective. To identify macrophage-independent sources of transforming growth factor [beta]1 (TGF[beta]1) production during monosodium urate monohydrate (MSU) crystal-induced inflammation and to determine how TGF[beta]1 alters MSU crystal-recruited neutrophil functions.

Methods. C57BL/6J mice were injected intraperitoneally with MSU crystals with or without TGF[beta]1-neutralizing antibody. MSU crystal-recruited peritoneal and blood neutrophils were purified and cultured ex vivo. Peritoneal neutrophils were treated with the caspase inhibitor Q-VD-OPh, anti-TGF[beta]1 antibody, or fluorochrome-labeled apoptotic neutrophils. Neutrophils were analyzed for expression of annexin V, caspase 3, and TGF[beta]1 by flow cytometry or fluorescence microscopy, for superoxide production using the redox-sensitive dye water-soluble tetrazolium 1, and for TGF[beta]1 and interleukin-1[beta] (IL-1[beta]) production by enzyme-linked immunosorbent assay.

Results. Eighteen hours after MSU crystal administration in vivo, TGF[beta]1 levels were elevated in peritoneal lavage fluids, and a significant number of peritoneal neutrophils were TGF[beta]1 . Purified blood or peritoneal neutrophils cultured ex vivo showed TGF[beta]1 neutrophils coexpressing the apoptosis marker caspase 3 and increased TGF[beta]1 production, both of which dropped following inhibition of apoptosis. Live neutrophils that had phagocytosed apoptotic neutrophils showed greatest TGF[beta]1 expression. Superoxide production by purified MSU crystal-recruited neutrophils ex vivo was enhanced by anti-TGF[beta]1 antibody treatment. Neutrophils purified from the peritoneum of MSU crystal-challenged mice treated with anti-TGF[beta]1 antibody produced elevated levels of superoxide, but neutrophil IL-1[beta] production was unaffected.

Conclusion. Neutrophil cannibalism and TGF[beta]1 production have the potential to make a significant contribution to the controlled resolution of neutrophil-driven inflammatory diseases such as gout.

(C) 2013, American College of Rheumatology