Response to 'Plasma proteins present in osteoarthritic synovial fluid can stimulate cytokine production via Toll-like receptor 4'
© BioMed Central Ltd 2012
Published: 12 September 2012
We read with great interest the article by Sohn and colleagues published in the February 2012 issue of Arthritis Research & Therapy . Using proteomic analysis, the authors were able to show that plasma proteins present in osteoarthritic synovial fluid are able to induce inflammatory cytokine production via interaction with Toll-like receptor 4, thus contributing to the low-grade inflammation associated with osteoarthritis.
We would like to add some observations concerning our data on the immunomodulatory effect of plasma on inflammation induced by calcium pyrophosphate crystals, which are considered danger signals to the innate immune system and, in osteoarthritis, provoke inflammation inducing the production and the release of proinflammatory mediators .
When calcium crystals are used in vitro, cells need to be preactivated with phorbol myristate acetate or, less frequently, with lipopolysaccharide because pure crystals alone are unable to induce IL-1β. In vivo, various plasma proteins coating onto the crystal surface have been shown to enhance phagocytic recognition of crystals by cells , leading to activation of some inflammatory pathways such as NALP-3 inflammasomes .
Fibrinogen has been shown to possess both inflammatory and anti-inflammatory properties depending on its concentration, and the effect is mediated by Toll-like receptor 4 . In our case, fibrinogen showed a direct effect both on cells and on crystals, with an overall effect on the modulation of inflammation.
Our results prompt us to speculate that fibrinogen is able to stimulate/modulate the inflammatory response to calcium crystals.
The authors are grateful to Mrs Linda Inverso Moretti for editing the English version of this manuscript
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