title: Safe disposal of inflammatory monosodium urate monohydrate crystals by differentiated macrophages.
abstract: OBJECTIVE
  Although monosodium urate monohydrate (MSU) crystals have been recognized since the 18th century as the etiologic agent of gout, it is still unknown why certain hyperuricemic individuals remain asymptomatic, and how an acute attack of gout spontaneously resolves. We hypothesized that mononuclear phagocytes hold the key to these questions, and that the state of monocyte/macrophage differentiation is critical.
  
  
  METHODS
  Human peripheral blood monocytes were differentiated for 1-7 days in vitro and examined with respect to 1) uptake of MSU crystals, 2) expression of macrophage, dendritic cell, and activation markers, 3) secretion of tumor necrosis factor alpha (TNFalpha), interleukin 1beta (IL-1beta), IL-6, and IL-10, 4) activation of endothelial E-selectin expression, and 5) enhancement of secondary neutrophil recruitment by endothelial cells.
  
  
  RESULTS
  MSU crystals induced TNFalpha, IL-1beta, and IL-6 (but not IL-10) secretion in undifferentiated monocytes, which in turn promoted endothelial cell E-selectin expression and secondary neutrophil capture under shear flow. In contrast, differentiation over 3-5 days led to development of a noninflammatory phenotype characterized by a lack of proinflammatory cytokine secretion, lack of endothelial cell activation, and lack of secondary neutrophil recruitment. Acquisition of the noninflammatory phenotype correlated with expression of macrophage antigen but not with expression of dendritic cell marker or activation marker. Monocytes and macrophages were similarly phagocytic, and a control particle, zymosan, elicited secretion of the full panel of cytokines in both cell types. However, coincubation with MSU led to a significant suppression of zymosan-induced TNFalpha secretion (P = 0.009) from macrophages but not monocytes.
  
  
  CONCLUSIONS
  These findings imply that differentiated macrophages provide a safe-disposal mechanism for the removal of inflammatory urate crystals. This may be of clinical relevance to the maintenance of asymptomatic hyperuricemia and the resolution of acute gout.
authors.affiliation: British Heart Foundation Cardiovascular Medicine Unit, National Heart and Lung Institute, London, UK.
authors.forename: R Clive
authors.initials: RC
authors.lastname: Landis
authors.forename: Darshna R
authors.initials: DR
authors.lastname: Yagnik
authors.forename: Oliver
authors.initials: O
authors.lastname: Florey
authors.forename: Pandelis
authors.initials: P
authors.lastname: Philippidis
authors.forename: Vivien
authors.initials: V
authors.lastname: Emons
authors.forename: Justin C
authors.initials: JC
authors.lastname: Mason
authors.forename: Dorian O
authors.initials: DO
authors.lastname: Haskard
mesh_terms: D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D003460:Crystallization; D019040:E-Selectin / Q000032:analysis; D004730:Endothelium, Vascular; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism; D016753:Interleukin-10 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism; D018375:Neutrophil Activation / Q000502:physiology; D020556:Neutrophil Infiltration / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014527:Uric Acid / Q000493:pharmacokinetics
chemical_list: D019040:E-Selectin; D007375:Interleukin-1; D015850:Interleukin-6; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D014527:Uric Acid