title: Crystals, inflammation, and osteoarthritis.
abstract: OBJECTIVE
  Calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals are common components of osteoarthritic joint fluids and tissues. Why these crystals form and how they contribute to joint damage in osteoarthritis remain unclear. With renewed interest in inflammation as a key component of osteoarthritis the role of calcium-containing crystals in this common disease warrants re-examination.
  
  
  RESULTS
  There is ample evidence supporting a pathogenic role for inflammation in osteoarthritis, and the innate immune system likely participates in this inflammatory process. Recent work reinforces the almost universal existence of calcium-containing crystals in tissues from patients with end-stage osteoarthritis. Calcium-containing crystals may contribute to inflammation in osteoarthritis tissues through their direct interactions with components of the innate immune system, as well as by inducing or amplifying other inflammatory signals.
  
  
  CONCLUSIONS
  There is increasing evidence that calcium-containing crystals contribute to osteoarthritis and their inflammatory properties may mediate detrimental effects through innate immunity signals. Calcium-containing crystals may thus represent important therapeutic targets in osteoarthritis.
authors.affiliation: Division of Rheumatology, Department of Medicine, Medical College of Wisconsin, and the Zablocki VA Medical Center, Milwaukee, Wisconsin, USA. ann.rosenthal@va.gov
authors.forename: Ann K
authors.initials: AK
authors.lastname: Rosenthal
mesh_terms: D002131:Calcium Pyrophosphate / Q000032:analysis*; D006801:Humans; D007249:Inflammation / Q000150:complications*; D010003:Osteoarthritis / Q000150:complications* / Q000175:diagnosis; D013582:Synovial Fluid / Q000737:chemistry*
chemical_list: D002131:Calcium Pyrophosphate